1WTNT44 KNHC 212051 2TCDAT4 3 4TROPICAL STORM ISAAC DISCUSSION NUMBER 3 5NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 6500 PM AST TUE AUG 21 2012 7 8AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE 9DEPRESSION REPORTED 44-KT FLIGHT-LEVEL WINDS AT 1000 FT TO THE 10NORTHEAST OF THE CENTER...AS WELL AS BIAS-CORRECTED SFMR SURFACE 11WINDS ESTIMATES OF 35 KT. THE MINIMUM CENTRAL PRESSURE WAS NEAR 121005 MB. BASED ON THESE DATA...THE DEPRESSION IS UPGRADED TO 13TROPICAL STORM ISAAC. DESPITE THE UPGRADE...THE CYCLONE REMAINS 14SOMEWHAT DISORGANIZED...WITH THE LOW-LEVEL CENTER PARTLY EXPOSED TO 15THE NORTH OF THE MAIN CONVECTIVE MASS. 16 17THE LOW-LEVEL CENTER HAS NUDGED NORTHWARD DURING THE AFTERNOON...BUT 18THE LONGER TERM MOTION IS 275/15. ISAAC REMAINS SOUTH OF A 19DEEP-LAYER SUBTROPICAL RIDGE THAT IS FORECAST TO REMAIN INTACT 20FOR THE NEXT 72 HR...WHICH SHOULD KEEP THE CYCLONE MOVING GENERALLY 21WESTWARD AS SHOWN BY THE TIGHTLY CLUSTERED TRACK MODEL GUIDANCE. 22AFTER THAT...THE GLOBAL MODELS CONTINUE TO FORECAST A SHORTWAVE 23TROUGH TO DIG SOUTHWARD OVER THE SOUTHEASTERN U.S. AND THE GULF OF 24MEXICO...WHICH IS EXPECTED TO WEAKEN THE RIDGE ACROSS FLORIDA AND 25THE BAHAMAS. THIS SHOULD ALLOW THE CYCLONE TO TURN WEST- 26NORTHWESTWARD AND SLOW DOWN OVER THE NORTH-CENTRAL CARIBBEAN SEA AND 27THE GREATER ANTILLES. THE GUIDANCE HAS BECOME LESS CONSISTENT 28SINCE THE PREVIOUS ADVISORY. WHILE THE CENTER OF THE GUIDANCE 29ENVELOPE HAS CHANGED LITTLE...THE ECMWF HAS SHIFTED WELL TO THE 30LEFT OF ITS PREVIOUS FORECAST AND NOW CALLS FOR A WESTWARD MOTION 31AFTER ISAAC PASSES HISPANIOLA. THE GFS ENSEMBLES HAVE ALSO SHIFTED 32WESTWARD...ALTHOUGH THE ENSEMBLE MEAN STILL LIES NEAR THE FORECAST 33TRACK. THE NEW TRACK IS NUDGED A LITTLE TO THE NORTH OF THE 34PREVIOUS TRACK BEFORE 72 HR...AND THEN IS NUDGED A LITTLE TO THE 35RIGHT THEREAFTER. THE TRACK FORECAST AFTER 72 HR LIES NEAR THE 36LEFT EDGE OF THE GUIDANCE ENVELOPE...WITH ONLY THE ECMWF WELL TO 37THE LEFT OF THE CURRENT FORECAST. USERS ARE CAUTIONED THAT FIVE-DAY 38TRACK ERRORS AVERAGE ABOUT 225 N MI. 39 40ISAAC CONTINUES TO EXPERIENCE SOME LIGHT NORTHEASTERLY VERTICAL WIND 41SHEAR...AND IT MAY NOT YET HAVE FULLY MIXED OUT THE DRY AIR THAT 42HAS BEEN AFFECTING IT. THE SHEAR IS FORECAST TO DIMINISH IN 12-24 43HR...WHICH SHOULD ALLOW SOME STRENGTHENING. THAT BEING SAID...THE 44GFDL AND HWRF MODELS HAVE BACKED OFF ON THEIR FORECASTS OF 45INTENSIFICATION...AND THE SHIPS AND LGEM MODELS ARE ALSO LESS 46BULLISH. BASED ON THIS...THE NEW INTENSITY FORECAST SHOWS A LITTLE 47LESS STRENGTHENING THAN THE PREVIOUS ADVISORY. THE INTENSITY 48FORECAST AFTER 72 HR HAS AGAIN BEEN REDUCED DUE TO THE FORECAST 49TRACK SHOWING INCREASED LAND INTERACTION WITH HISPANIOLA AND CUBA. 50 51 52 53 54FORECAST POSITIONS AND MAX WINDS 55 56INIT 21/2100Z 15.4N 53.9W 35 KT 40 MPH 57 12H 22/0600Z 15.6N 56.4W 40 KT 45 MPH 58 24H 22/1800Z 15.9N 59.8W 45 KT 50 MPH 59 36H 23/0600Z 16.3N 63.1W 50 KT 60 MPH 60 48H 23/1800Z 16.6N 66.3W 65 KT 75 MPH 61 72H 24/1800Z 17.0N 71.0W 75 KT 85 MPH 62 96H 25/1800Z 19.5N 75.0W 75 KT 85 MPH 63120H 26/1800Z 21.5N 78.0W 65 KT 75 MPH...INLAND 64 65$$ 66FORECASTER BEVEN 67 68 69WTNT44 KNHC 220249 70TCDAT4 71 72TROPICAL STORM ISAAC DISCUSSION NUMBER 4 73NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 741100 PM AST TUE AUG 21 2012 75 76THERE HAS BEEN NO AERIAL RECONNAISSANCE INTO ISAAC RECENTLY...BUT 77THE CLOUD PATTERN OF THE STORM HAS NOT BECOME SIGNIFICANTLY BETTER 78ORGANIZED OVER THE PAST FEW HOURS. THE INTENSITY IS HELD AT 35 KT 79WHICH IS IN AGREEMENT WITH A DVORAK INTENSITY ESTIMATE FROM TAFB. 80ANOTHER HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE ISAAC 81AT AROUND 0600 UTC. 82 83THERE IS SOME SPREAD IN CENTER FIXES...BUT BASED ON GEOSTATIONARY 84AND MICROWAVE IMAGERY THE INITIAL MOTION REMAINS ABOUT THE 85SAME...275/16. A WELL-DEFINED MID-TROPOSPHERIC RIDGE TO THE NORTH 86OF THE TROPICAL CYCLONE SHOULD MAINTAIN THE WESTWARD TRACK FOR THE 87NEXT COUPLE OF DAYS. LATER IN THE FORECAST PERIOD...GLOBAL MODELS 88DEPICT ISAAC NEARING A BREAK IN THE RIDGE NEAR FLORIDA. 89CONSEQUENTLY THE FORWARD SPEED IS LIKELY TO SLOW...AND THE HEADING 90TO GRADUALLY TURN TOWARD THE RIGHT...IN THE LATTER HALF OF THE 91FORECAST PERIOD. ALTHOUGH THE GFS HAS SHIFTED JUST A BIT TO THE 92NORTH OF ITS PREVIOUS FORECAST...OVERALL THE TRACK GUIDANCE HAS NOT 93CHANGED MUCH SINCE THE PREVIOUS CYCLE. THE OFFICIAL FORECAST IS 94VERY CLOSE TO THE LATEST HWRF TRACK AND NOT FAR FROM THE DYNAMICAL 95CONSENSUS. 96 97WATER VAPOR IMAGERY SUGGESTS THAT EAST-NORTHEASTERLY SHEAR IS 98CURRENTLY AFFECTING ISAAC...BUT THE DYNAMICAL GUIDANCE PREDICTS A 99DECREASE IN SHEAR WITH UPPER-LEVEL ANTICYCLONIC FLOW OVER THE 100TROPICAL CYCLONE DURING THE NEXT SEVERAL DAYS. THEREFORE 101STRENGTHENING IS ANTICIPATED...AND ISAAC COULD BECOME A HURRICANE 102WITHIN THE NEXT COUPLE OF DAYS. LATER ON...THE INTENSITY FORECAST 103IS COMPLICATED BY HOW MUCH THE CORE OF THE SYSTEM INTERACTS WITH 104THE MOUNTAINOUS LAND MASSES OF HISPANIOLA AND EASTERN CUBA. THE 105OFFICIAL WIND SPEED FORECAST IS FAIRLY CLOSE TO THE STATISTICAL- 106DYNAMICAL GUIDANCE FOR THE FIRST 48 HOURS AND THEN TRIES TO TAKE 107INTO ACCOUNT THE LAND INTERACTION. NEEDLESS TO SAY...THERE IS 108CONSIDERABLE UNCERTAINTY IN THE INTENSITY OF ISAAC IN THE 3 TO 5 109DAY TIME FRAME. 110 111FORECAST POSITIONS AND MAX WINDS 112 113INIT 22/0300Z 15.6N 55.6W 35 KT 40 MPH 114 12H 22/1200Z 15.8N 58.1W 40 KT 45 MPH 115 24H 23/0000Z 16.2N 61.2W 45 KT 50 MPH 116 36H 23/1200Z 16.7N 64.3W 55 KT 65 MPH 117 48H 24/0000Z 17.1N 67.1W 65 KT 75 MPH 118 72H 25/0000Z 18.3N 72.0W 65 KT 75 MPH...INLAND 119 96H 26/0000Z 20.5N 76.0W 70 KT 80 MPH...INLAND 120120H 27/0000Z 23.0N 79.0W 70 KT 80 MPH...OVER WATER 121 122$$ 123FORECASTER PASCH 124 125 126WTNT44 KNHC 220851 127TCDAT4 128 129TROPICAL STORM ISAAC DISCUSSION NUMBER 5 130NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 131500 AM AST WED AUG 22 2012 132 133SATELLITE IMAGERY INDICATES A LARGE CENTRAL DENSE OVERCAST FEATURE 134HAS DEVELOPED OVER THE LOW-LEVEL CENTER...WHICH INCLUDES SOME COLD 135CLOUD TOPS OF -82 TO -86C VERY NEAR THE CENTER. HOWEVER...THE SHARP 136INCREASE IN INNER-CORE CONVECTION HAS NOT YET TRANSLATED INTO ANY 137SIGNIFICANT INTENSIFICATION. AN AIR FORCE RESERVE RECONNAISSANCE 138AIRCRAFT INVESTIGATING ISAAC THIS MORNING HAS ONLY FOUND THE 139CENTRAL PRESSURE TO BE 1003 MB AND 850 MB FLIGHT-LEVEL WINDS OF 47 140KT...WHICH EQUATES TO ABOUT A 40-KT INTENSITY ESTIMATE. SFMR WINDS 141IN VERY HEAVY RAIN HAVE BEEN AS HIGH AS 61 KT. THE BIAS-ADJUSTED 142SFMR WINDS HAVE BEEN RUNNING AS HIGH AS 54 KT...BUT EVEN THOSE 143VALUES APPEAR TO BE INFLATED. UNTIL THE AIRCRAFT COMPLETES ITS 144MISSION... THE INITIAL INTENSITY WILL REMAIN AT 40 KT BASED ON THE 1451003 MB PRESSURE-WIND RELATIONSHIP. 146 147THE INITIAL MOTION ESTIMATE IS 270/15 KT. THE INITIAL POSITION IS A 148BLEND OF THE RECON FIXES AND SATELLITE POSITIONS...AND CONTINUITY 149WITH PREVIOUS FORECAST TRACK. THERE IS NO SIGNIFICANT CHANGE TO THE 150PREVIOUS FORECAST TRACK OR REASONING. THE EAST-WEST ORIENTED 151SUBTROPICAL RIDGE TO THE NORTH OF ISAAC ALONG 30N LATITUDE IS 152FORECAST BY ALL OF THE GLOBAL MODELS TO REMAIN INTACT ACROSS 153FLORIDA AND THE SOUTHEASTERN U.S. THROUGH 72 HOURS OR SO. AFTER 154THAT...A BROAD MID- TO UPPER-LEVEL TROUGH CURRENTLY LOCATED OVER 155THE CENTRAL U.S. FROM THE GREAT LAKES SOUTHWARD TO THE CENTRAL GULF 156COAST IS EXPECTED TO DIG SOUTHWARD OVER THE NEXT 24 HOURS BEFORE 157MOVING EASTWARD. THIS SHOULD RESULT IN AN EROSION OF THE RIDGE 158ACROSS THE EASTERN GULF OF MEXICO AND THE SOUTHEASTERN U.S. 159INCLUDING FLORIDA AND THE NORTHWESTERN BAHAMAS. THIS DEVELOPING 160WEAKNESS IN THE RIDGE SHOULD ALLOW ISAAC TO TURN NORTHWESTWARD 161ACROSS EASTERN AND CENTRAL CUBA BY DAYS 4 AND 5. THE NHC MODEL 162GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH 163THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF 164BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY 165OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE 166SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY 167DEEPER CYCLONE DEPICTED IN THE MODELS. 168 169SHEAR ANALYSES FROM THE GFS-BASED SHIPS INTENSITY MODEL AND UW-CIMSS 170INDICATE BOTH THE DEEP-LAYER AND MID-LEVEL SHEAR VALUES HAVE 171DROPPED BELOW 10 KT...WHICH HAS FINALLY ALLOWED DEEP CONVECTION TO 172DEVELOP AND PERSIST OVER THE LOW-LEVEL CENTER. THE SHEAR IS 173FORECAST TO GRADUALLY DECREASE TO VALUES BELOW 5 KT BY 24 HOURS... 174WHICH SHOULD ALLOW ISAAC TO STRENGTHEN TO A HURRICANE BY 48 HOURS. 175AT 72 AND 96 HOURS...THE INTENSITY HAS BEEN DECREASED DUE TO 176EXPECTED LAND INTERACTION WITH HAITI AND EASTERN CUBA. AFTER 96 177HOURS...HOWEVER...ISAAC SHOULD BE MOVING BACK OVER THE VERY WARM 178WATER BETWEEN CUBA AND FLORIDA. WITH SEA-SURFACE TEMPERATURES 179EXPECTED TO BE NEAR 30C AND THE GFS AND UKMET MODELS DEPICTING A 180EXTENSIVE UPPER-LEVEL OUTFLOW REGIME COMPLETE WITH DUAL OUTFLOW 181CHANNELS TO THE NORTHWEST AND SOUTHEAST...STRENGTHENING APPEARS 182LIKELY. THE OFFICIAL INTENSITY REMAINS ON THE CONSERVATIVE SIDE DUE 183TO UNCERTAINTY IN HOW LONG AND HOW MUCH ISAAC WILL INTERACT WITH 184HISPANIOLA AND CUBA...AND IS CLOSE TO A BLEND OF THE SHIPS... 185DECAY-SHIPS...AND LGEM STATISTICAL-DYNAMICAL INTENSITY MODELS. 186 187FORECAST POSITIONS AND MAX WINDS 188 189INIT 22/0900Z 15.5N 57.3W 40 KT 45 MPH 190 12H 22/1800Z 15.9N 59.7W 45 KT 50 MPH 191 24H 23/0600Z 16.3N 62.8W 55 KT 65 MPH 192 36H 23/1800Z 16.8N 65.7W 65 KT 75 MPH 193 48H 24/0600Z 17.3N 68.4W 75 KT 85 MPH 194 72H 25/0600Z 18.8N 73.2W 65 KT 75 MPH...OVER WATER 195 96H 26/0600Z 21.8N 77.1W 65 KT 75 MPH...OVER WATER 196120H 27/0600Z 24.8N 80.0W 80 KT 90 MPH 197 198$$ 199FORECASTER STEWART 200 201 202WTNT44 KNHC 221449 203TCDAT4 204 205TROPICAL STORM ISAAC DISCUSSION NUMBER 6 206NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 2071100 AM AST WED AUG 22 2012 208 209THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT MONITORING ISAAC 210DURING THE NIGHT REPORTED THAT THE INNER CORE WIND FIELD BECAME 211DISORGANIZED AFTER 0600 UTC. A COUPLE OF MICROWAVE OVERPASSES 212SUGGEST THAT THE CIRCULATION CENTER BECAME ELONGATED DURING THIS 213TIME....AND THE CENTER IS NOT READILY APPARENT IN FRENCH RADAR DATA 214FROM MARTINIQUE AND GUADELOUPE. THE INITIAL INTENSITY IS HELD AT 21540 KT BASED ON AIRCRAFT-REPORTED WINDS NORTH OF THE CENTER. WHILE 216THE CENTRAL CORE IS DISORGANIZED...THE OVERALL STRUCTURE OF THE 217STORM IS IMPROVING...AS SATELLITE IMAGERY SHOWS A LARGE OUTER BAND 218FORMING AROUND THE CENTRAL CONVECTIVE FEATURE. 219 220THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 280/15...AS IT IS UNCLEAR 221HOW MUCH OF THE OBSERVED NORTHWARD NUDGE WAS DUE TO RE-FORMATION OF 222THE CENTER. OTHER THAN THAT...THERE IS NO SIGNIFICANT CHANGE TO THE 223PREVIOUS FORECAST TRACK OR REASONING DURING THE FIRST 48-72 HR OF 224THE TRACK FORECAST. THE EAST-WEST ORIENTED SUBTROPICAL RIDGE TO THE 225NORTH OF ISAAC ALONG 30N LATITUDE IS FORECAST BY ALL OF THE GLOBAL 226MODELS TO REMAIN INTACT ACROSS FLORIDA AND THE SOUTHEASTERN U.S. 227DURING THAT TIME. THIS EARLY PART OF THE FORECAST TRACK IS AN 228UPDATE OF THE PREVIOUS FORECAST. AFTER THAT TIME...THE RIDGE IS 229EXPECTED TO WEAKEN SOMEWHAT AS A MID/UPPER-LEVEL TROUGH MOVES ONTO 230THE EASTERN UNITED STATES. THE MODELS DIVERGE ON THEIR FORECASTS 231OF THE RIDGE. THE ECMWF DOES NOT BREAK THE RIDGE...AND THUS 232FORECASTS A MORE WESTWARD MOTION NEAR OR SOUTH OF CUBA. THE 233CANADIAN AND NOGAPS HAVE A LARGE BREAK IN THE RIDGE AND TURN ISAAC 234NORTHWARD EAST OF FLORIDA. THE UKMET HAS A BREAK IN THE RIDGE OVER 235THE NORTHERN GULF COAST AND MOVES THE CYCLONE OVER THE FLORIDA 236PENINSULA. THE GFS SHOWS A BREAK IN THE RIDGE EAST OF FLORIDA... 237BUT FORECASTS ISAAC TO BYPASS THE BREAK AND MOVE NEAR THE SOUTHWEST 238COAST OF FLORIDA. THIS DECREASED-CONFIDENCE PORTION OF THE 239FORECAST TRACK IS SHIFTED A LITTLE WEST OF THE PREVIOUS TRACK TO 240LIE NEAR THE CONSENSUS MODELS. 241 242WATER VAPOR IMAGERY AND MICROWAVE TOTAL PRECIPITABLE WATER DATA SHOW 243DRY AIR TO THE NORTHEAST OF ISAAC...AND A LACK OF CONVECTION IN 244THIS AREA SUGGESTS SOME OF THIS AIR IS ENTRAINING INTO THE CYCLONE. 245OTHERWISE...ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR 246INTENSIFICATION UNTIL THE CENTER REACHES HISPANIOLA IN ABOUT 48 HR. 247AFTER THAT...THE INTENSITY WILL BE DETERMINED BY HOW MUCH TIME ISAAC 248SPENDS OVER LAND. THE NEW FORECAST IS SIMILAR TO THE PREVIOUS 249FORECAST THROUGH 48 HR...THEN IS REDUCED A LITTLE BASED ON 250INCREASED LAND INTERACTION IN THE NEW FORECAST TRACK. 251 252A HURRICANE WARNING WILL LIKELY BE REQUIRED FOR PORTIONS OF THE 253DOMINICAN REPUBLIC THIS AFTERNOON. IT SHOULD BE NOTED THAT WHILE 254NONE OF THE FORECAST POINTS ARE OVER LAND...THE CYCLONE IS FORECAST 255TO MOVE OVER HISPANIOLA AND CUBA FROM 48-96 HR. 256 257 258FORECAST POSITIONS AND MAX WINDS 259 260INIT 22/1500Z 15.9N 59.3W 40 KT 45 MPH 261 12H 23/0000Z 16.3N 61.8W 45 KT 50 MPH 262 24H 23/1200Z 16.8N 64.8W 50 KT 60 MPH 263 36H 24/0000Z 17.3N 67.8W 60 KT 70 MPH 264 48H 24/1200Z 17.8N 70.3W 75 KT 85 MPH 265 72H 25/1200Z 19.5N 74.5W 60 KT 70 MPH 266 96H 26/1200Z 22.5N 78.5W 60 KT 70 MPH 267120H 27/1200Z 25.5N 81.5W 70 KT 80 MPH 268 269$$ 270FORECASTER BEVEN 271 272 273WTNT44 KNHC 222039 274TCDAT4 275 276TROPICAL STORM ISAAC DISCUSSION NUMBER 7 277NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 278500 PM AST WED AUG 22 2012 279 280SATELLITE...AIRCRAFT...RADAR...AND SURFACE OBSERVATIONS INDICATE 281THAT ISAAC HAS A BROAD CENTRAL AREA OF LIGHT WINDS WITH MULTIPLE 282VORTICITY MAXIMA EMBEDDED. THE LOWEST PRESSURES ARE IN AN AREA 283NEAR GUADELOUPE...WHICH IS USED AS THE CURRENT CENTER SINCE IT HAS 284SOME CONTINUITY WITH THE CENTER PREVIOUSLY BEING TRACKED. 285HOWEVER...THE MEAN CENTER IS LIKELY TO THE SOUTHEAST OF THE 286ADVISORY POSITION. SOME ADJUSTMENT OF THE CENTER POSITION MAY BE 287NECESSARY WHEN THE CENTRAL CORE AGAIN CONSOLIDATES. THE INITIAL 288INTENSITY IS HELD AT 40 KT...ALTHOUGH THE HURRICANE HUNTER AIRCRAFT 289DATA SUGGESTS THIS COULD BE GENEROUS. 290 291THE INITIAL MOTION IS NOW A SOMEWHAT UNCERTAIN 280/19. OTHER THAN 292THE CENTER POSITION ISSUES...THERE IS NO SIGNIFICANT CHANGE TO THE 293FORECAST REASONING DURING THE FIRST 48 HR OF THE TRACK FORECAST. THE 294EAST-WEST ORIENTED SUBTROPICAL RIDGE TO THE NORTH OF ISAAC ALONG 29530N LATITUDE IS FORECAST BY ALL OF THE GLOBAL MODELS TO REMAIN 296INTACT ACROSS FLORIDA AND THE SOUTHEASTERN U.S. DURING THAT TIME. 297THIS EARLY PART OF THE FORECAST TRACK IS SHIFTED A LITTLE TO THE 298SOUTH OF THE PREVIOUS FORECAST BASED ON THE OBSERVED POSITION AND 299MOTION. AFTER 48 HR...THE RIDGE IS EXPECTED TO WEAKEN AS A 300MID/UPPER-LEVEL TROUGH MOVES ONTO THE EASTERN UNITED STATES. THE 301GLOBAL MODELS HAVE COME INTO BETTER AGREEMENT SINCE THE LAST 302ADVISORY...WITH THE NOGAPS AND CANADIAN MODELS SHIFTING TO THE WEST 303AND THE ECMWF TO THE NORTH. HOWEVER...THE ECMWF CONTINUES TO SHOW 304A STRONGER RIDGE...AND THUS SHOWS A MORE WESTERLY MOTION THAN THE 305OTHER MODELS. THE 72-120 HR PORTION OF THE FORECAST TRACK IS 306SIMILAR TO THE PREVIOUS FORECAST AND LIES NEAR THE CONSENSUS 307MODELS. THERE REMAINS CONSIDERABLE UNCERTAINTY AS TO WHICH PORTIONS 308OF FLORIDA...IF ANY...COULD BE AFFECTED BY ISAAC. 309 310WATER VAPOR IMAGERY AND MICROWAVE TOTAL PRECIPITABLE WATER DATA 311CONTINUE TO SHOW DRY AIR TO THE NORTHEAST OF ISAAC...AND A LACK OF 312CONVECTION IN THIS AREA SUGGESTS SOME OF THIS AIR IS ENTRAINING 313INTO THE CYCLONE AND DISRUPTING THE CONVECTIVE STRUCTURE. GIVEN 314THE CURRENT STRUCTURE...THE NEW INTENSITY FORECAST CALLS FOR LITTLE 315CHANGE IN STRENGTH FOR THE NEXT 12 HR...FOLLOWED BY INTENSIFICATION 316INTO A HURRICANE BY 48 HR SIMILAR TO THE PREVIOUS ADVISORY. AFTER 31748 HR...THE MAIN FACTOR CONTROLLING THE INTENSITY IS THE AMOUNT OF 318LAND INTERACTION. THIS LOW-CONFIDENCE PART OF THE INTENSITY 319FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY BUT ABOVE THE INTENSITY 320CONSENSUS. 321 322 323FORECAST POSITIONS AND MAX WINDS 324 325INIT 22/2100Z 16.0N 61.2W 40 KT 45 MPH 326 12H 23/0600Z 16.3N 63.6W 40 KT 45 MPH 327 24H 23/1800Z 16.7N 66.7W 50 KT 60 MPH 328 36H 24/0600Z 17.2N 69.4W 60 KT 70 MPH 329 48H 24/1800Z 17.9N 71.6W 70 KT 80 MPH...INLAND 330 72H 25/1800Z 20.5N 75.5W 60 KT 70 MPH...INLAND 331 96H 26/1800Z 23.5N 79.5W 60 KT 70 MPH...OVER WATER 332120H 27/1800Z 26.5N 82.5W 70 KT 80 MPH 333 334$$ 335FORECASTER BEVEN 336 337 338WTNT44 KNHC 230257 339TCDAT4 340 341TROPICAL STORM ISAAC DISCUSSION NUMBER 8 342NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 3431100 PM AST WED AUG 22 2012 344 345AN AIR FORCE HURRICANE HUNTER AIRCRAFT INVESTIGATED ISAAC SEVERAL 346HOURS AGO AND FOUND THAT THE CENTER WAS STILL NOT WELL-DEFINED AND 347THE INTENSITY ESTIMATE OF 40 KT WAS PROBABLY A LITTLE ON THE HIGH 348SIDE. HOWEVER...DROPSONDE DATA FROM A NOAA AIRCRAFT CURRENTLY 349INVESTIGATING THE STORM SUGGEST THAT THE CENTER HAS PROBABLY BECOME 350A LITTLE BETTER DEFINED AND THAT THE MINIMUM PRESSURE HAS DROPPED A 351BIT. THERE HAS ALSO BEEN AN INCREASE IN COLD-TOPPED CONVECTION 352NEAR AND OVER THE ESTIMATED CENTER SO THE CURRENT INTENSITY IS HELD 353AT 40 KT. ISAAC HAS DEVELOPED AN IMPRESSIVE UPPER-LEVEL OUTFLOW 354PATTERN AND DYNAMICAL GUIDANCE SHOWS THAT THE VERTICAL SHEAR SHOULD 355REMAIN WEAK DURING THE NEXT SEVERAL DAYS. THEREFORE THE PRIMARY 356IMPEDIMENT TO STRENGTHENING SHOULD BE THE INTERACTION WITH THE 357MOUNTAINOUS TERRAIN OF HISPANIOLA AND EASTERN CUBA. THE MOST 358RECENT RUNS OF THE HWRF AND GFDL SHOW SIMILAR AMOUNTS OF LAND 359INTERACTION BUT ARE NOT IN GOOD AGREEMENT ON THE INTENSITY FORECAST 360AS THE FORMER MODEL SHOWS MUCH LESS STRENGTHENING THAN THE LATTER. 361THE OFFICIAL WIND SPEED FORECAST IS IN REASONABLE AGREEMENT WITH 362THE LATEST STATISTICAL-DYNAMICAL GUIDANCE. 363 364AFTER A SLIGHT SOUTHWARD RELOCATION OF THE CENTER...THE INITIAL 365MOTION CONTINUES BASICALLY WESTWARD OR 270/17. ISAAC SHOULD 366CONTINUE TO MOVE WESTWARD TO WEST-NORTHWESTWARD FOR THE NEXT COUPLE 367OF DAYS ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE. THE 368GLOBAL MODELS CONTINUE TO DEPICT A BREAK IN THE RIDGE IN THE 369VICINITY OF FLORIDA IN SEVERAL DAYS...WHICH SHOULD INDUCE A MORE 370NORTHWARD COMPONENT OF MOTION. THE ECMWF MODEL SHOWS LESS OF A 371BREAK IN THE RIDGE THAN THE GFS SOLUTION. CONSEQUENTLY...THE ECMWF 372TRACK IS SOMEWHAT TO THE SOUTHWEST OF MOST OF THE OTHER TRACK 373MODELS WHICH WOULD LESSEN THE THREAT TO FLORIDA. THE OFFICIAL 374TRACK FORECAST FOR THIS ADVISORY IS QUITE CLOSE TO THE PREVIOUS ONE 375AND ALSO VERY CLOSE TO THE DYNAMICAL MODEL CONSENSUS. 376 377FORECAST POSITIONS AND MAX WINDS 378 379INIT 23/0300Z 15.8N 63.0W 40 KT 45 MPH 380 12H 23/1200Z 16.2N 65.4W 45 KT 50 MPH 381 24H 24/0000Z 16.9N 68.1W 55 KT 65 MPH 382 36H 24/1200Z 17.5N 70.5W 65 KT 75 MPH 383 48H 25/0000Z 18.6N 72.7W 55 KT 65 MPH 384 72H 26/0000Z 21.5N 77.0W 60 KT 70 MPH...ON NORTH COAST OF CUBA 385 96H 27/0000Z 24.0N 80.5W 65 KT 75 MPH 386120H 28/0000Z 27.0N 83.5W 70 KT 80 MPH 387 388$$ 389FORECASTER PASCH 390 391 392WTNT44 KNHC 230858 393TCDAT4 394 395TROPICAL STORM ISAAC DISCUSSION NUMBER 9 396NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 397500 AM AST THU AUG 23 2012 398 399AN AIR FORCE RECONNAISSANCE AIRCRAFT INVESTIGATING ISAAC THIS 400MORNING HAS FOUND A POORLY DEFINED INNER CORE WITH A LARGE AREA OF 401LIGHT WINDS AROUND A CENTER...WHICH IS SIMILAR TO WHAT AN EARLIER 402NOAA RESEARCH MISSION INDICATED. RADAR DATA FROM GUADELOUPE AND SAN 403JUAN ALSO INDICATE A POORLY DEFINED INNER CORE CONVECTIVE PATTERN. 404RATHER THAN INITIALIZE THE CENTER OF ISAAC WELL TO THE SOUTH OF THE 405PREVIOUS TRACK...I HAVE OPTED TO USE A BLEND OF THE RECON FIXES... 406SATELLITE IMAGERY...DATA FROM NEARBY NOAA BUOY 42060...AND A 06Z 407CONSENSUS FORECAST POSITION FROM THE GFS...ECMWF...AND UKMET 408MODELS. THE INITIAL INTENSITY WAS ALSO DECREASED TO 35 KT BASED ON 409DATA FROM THE RECON AIRCRAFT AND NOAA BUOY 42060. 410 411THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 270/12 KT. THE 00Z 412GFS...ECMWF...AND UKMET MODELS DID AN OUTSTANDING JOB PREDICTING 413THE RECENT SOUTHWESTWARD JOG OR REFORMATION OF THE CENTER OF ISAAC. 414THOSE SAME MODELS ARE ALSO FORECASTING ISAAC TO MAKE A SHARP JOG TO 415THE NORTHWEST OVER THE NEXT 12-24 HOURS...AND THEN STEADY OFF ON A 416GENERAL WEST-NORTHWESTWARD MOTION THROUGH 48 HOURS. AFTER THAT... 417THE GLOBAL AND REGIONAL MODELS HAVE COME INTO BETTER AGREEMENT ON 418ISAAC MOVING NORTHWESTWARD TOWARD A BREAK IN THE SUBTROPICAL RIDGE 419THAT IS FORECAST TO DEVELOP AFTER 72 HOURS ACROSS FLORIDA AND THE 420EASTERN GULF OF MEXICO. THE ECMWF MODEL HAS CONTINUED ITS EASTWARD 421SHIFT OVER THE PAST 36 HOURS...AND EVEN THE LATEST NOGAPS AND 422CANADIAN MODEL RUNS HAVE SHIFTED WELL TO THE WEST ACROSS THE 423FLORIDA PENINSULA ARE NOW NO LONGER CONSIDERED TO BE OUTLIERS. DUE 424TO LESS SPREAD IN THE LATEST NHC MODEL GUIDANCE...AND THE FACT THAT 425ECMWF HAS SHIFTED CLOSER TO THE PREVIOUS FORECAST AT DAYS 4 AND 4265...THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS 427ADVISORY TRACK...AND IS CLOSE TO THE DYNAMICAL CONSENSUS MODELS 428TVCA AND TV15. 429 430UPPER-AIR DATA FROM ST. MAARTEN AT 00Z CONFIRMS THE DRY AIR IN THE 431MID-LEVELS OF THE ATMOSPHERE BETWEEN 600 AND 300 MB AS ALLUDED TO 432IN PREVIOUS DISCUSSIONS. THIS LAYER OF VERY DRY AIR HAS BEEN 433HINDERING CONVECTIVE DEVELOPMENT IN THE NORTHEASTERN QUADRANT FOR 434THE PAST 3-4 DAYS. HOWEVER...THE GLOBAL MODELS ARE IN GOOD 435AGREEMENT ON THE DRY AIR MIXING OUT OVER THE NEXT 36 HOURS AND THE 436INNER CORE BECOMING QUITE MOIST...WHICH SHOULD ALLOW FOR SOME 437STEADY INTENSIFICATION TO OCCUR BEFORE ISAAC INTERACTS WITH THE 438MOUNTAINOUS TERRAIN OF HISPANIOLA. GIVEN THE IMPRESSIVE UPPER-LEVEL 439OUTFLOW PATTERN THAT THE CYCLONE HAS DEVELOPED...ISAAC IS STILL 440EXPECTED TO BECOME A HURRICANE BY 36 HOURS. AFTER THAT...HOWEVER... 441THE THE PRIMARY IMPEDIMENT TO STRENGTHENING WILL BE THE INTERACTION 442WITH THE LAND MASSES OF HISPANIOLA AND EASTERN CUBA. HOW MUCH THE 443INNER CORE OF ISAAC IS DISRUPTED WHILE OVER LAND WILL DETERMINE 444JUST HOW MUCH RE-STRENGTHENING WILL OCCUR ONCE THE CENTER MOVES 445BACK OVER WATER AFTER 72 HOURS. THE OFFICIAL INTENSITY FORECAST IS 446SIMILAR TO THE PREVIOUS FORECAST AND IS IN REASONABLE AGREEMENT 447WITH THE DECAY-SHIPS AND LGEM INTENSITY MODELS. 448 449FORECAST POSITIONS AND MAX WINDS 450 451INIT 23/0900Z 15.3N 64.0W 35 KT 40 MPH 452 12H 23/1800Z 16.2N 65.9W 40 KT 45 MPH 453 24H 24/0600Z 16.9N 68.4W 50 KT 60 MPH 454 36H 24/1800Z 17.8N 71.1W 65 KT 75 MPH 455 48H 25/0600Z 19.1N 73.4W 55 KT 65 MPH 456 72H 26/0600Z 21.8N 77.4W 60 KT 70 MPH...INLAND 457 96H 27/0600Z 24.4N 80.9W 65 KT 75 MPH...OVER WATER 458120H 28/0600Z 27.4N 83.7W 70 KT 80 MPH 459 460$$ 461FORECASTER STEWART 462 463 464WTNT44 KNHC 231453 465TCDAT4 466 467TROPICAL STORM ISAAC DISCUSSION NUMBER 10 468NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 4691100 AM AST THU AUG 23 2012 470 471THE SATELLITE APPEARANCE OF ISAAC HAS IMPROVED SOMEWHAT THIS 472MORNING...WITH MULTIPLE CONVECTIVE BANDS DEVELOPING AROUND THE 473CENTER. HOWEVER...REPORTS FROM AIR FORCE RESERVE AND NOAA 474HURRICANE HUNTER AIRCRAFT INDICATE THAT THE CENTRAL CORE OF ISAAC 475REMAINS POORLY ORGANIZED...WITH MULTIPLE LOW-LEVEL VORTICITY CENTERS 476ROTATING AROUND A LARGE AREA OF LIGHT WINDS. IN ADDITION...THE 477CENTER IN AIRCRAFT DATA IS NORTH OF THE CENTER SUGGESTED BY THE 478SATELLITE IMAGERY. A COMBINATION OF FLIGHT-LEVEL...DROPSONDE...AND 479SFMR WINDS SUGGEST THAT THE INITIAL INTENSITY IS NEAR 35 KT. 480 481THE OVERALL CIRCULATION OF ISAAC IS A LITTLE FARTHER SOUTH THAN 12 482HR AGO. HOWEVER...IT SEEMS TO HAVE RESUMED A WESTWARD MOTION AT 483ABOUT 13 KT. THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT THAT 484ISAAC SHOULD MOVE WEST-NORTHWESTWARD FOR THE NEXT 36-48 HR... 485STEERED BY THE SUBTROPICAL RIDGE TO THE NORTH. AFTER THAT...THE 486STORM SHOULD APPROACH A WEAKNESS OR BREAK IN THE RIDGE OVER FLORIDA 487AND THE EASTERN GULF OF MEXICO. THE NEW FORECAST TRACK IS SHIFTED A 488LITTLE TO THE WEST OF THE PREVIOUS TRACK BASED ON CURRENT POSITION 489AND LIES DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE NEAR THE 490CONSENSUS MODELS. IT SHOULD BE NOTED...THOUGH...THAT NEAR THE 96 491HR POINT THE GUIDANCE MODELS ARE SPREAD BETWEEN SOUTHEASTERN 492FLORIDA AND WESTERN CUBA...AND AT 120 HR THEY ARE BETWEEN 493NORTHEASTERN FLORIDA AND THE CENTRAL GULF OF MEXICO. THUS... 494SIGNIFICANT UNCERTAINTY REMAINS ABOUT THE THREAT ISAAC POSES TO 495FLORIDA. 496 497IN THE SHORT TERM...THE STRUCTURE OF ISAAC SUGGESTS THAT ONLY SLOW 498STRENGTHENING IS LIKELY. HOWEVER...THE ENVIRONMENTAL CONDITIONS 499ARE FAVORABLE FOR RAPID INTENSIFICATION...WHICH COULD OCCUR IF THE 500CYCLONE DEVELOPS A WELL-DEFINED INNER CORE. BASED ON THIS...THE 501INTENSITY FORECAST CONTINUES TO SHOW HURRICANE STRENGTH BEFORE THE 502SYSTEM REACHES HISPANIOLA IN ABOUT 36 HR. AFTER THAT...PASSAGE OVER 503HISPANIOLA AND CUBA SHOULD CAUSE SOME WEAKENING...FOLLOWED BY 504LITTLE CHANGE OF STRENGTH FROM 48-72 HR. THE INTENSITY FORECAST 505SHOWS A LITTLE MORE STRENGTHENING OVER THE GULF OF MEXICO DUE TO 506THE FORECAST TRACK BEING A LITTLE FARTHER FROM THE FLORIDA 507PENINSULA THAN BEFORE. THE INTENSITY FORECAST IS BASED ON A BLEND 508OF THE PREVIOUS FORECAST AND THE SHIPS/LGEM MODELS...AND IT IS WELL 509ABOVE THE INTENSITY CONSENSUS. 510 511 512FORECAST POSITIONS AND MAX WINDS 513 514INIT 23/1500Z 15.6N 65.4W 35 KT 40 MPH 515 12H 24/0000Z 16.1N 67.4W 40 KT 45 MPH 516 24H 24/1200Z 16.9N 70.0W 50 KT 60 MPH 517 36H 25/0000Z 18.0N 72.4W 65 KT 75 MPH 518 48H 25/1200Z 19.3N 74.6W 55 KT 65 MPH 519 72H 26/1200Z 22.0N 78.5W 55 KT 65 MPH...INLAND 520 96H 27/1200Z 24.5N 81.5W 65 KT 75 MPH...OVER WATER 521120H 28/1200Z 27.5N 84.5W 75 KT 85 MPH 522 523$$ 524FORECASTER BEVEN 525 526 527WTNT44 KNHC 232055 528TCDAT4 529 530TROPICAL STORM ISAAC DISCUSSION NUMBER 11 531NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 532500 PM AST THU AUG 23 2012 533 534LOCATING THE CENTER OF ISAAC IS A BIT PROBLEMATIC THIS AFTERNOON. 535WHILE THE CYCLONE HAS A LARGE AND WELL-DEFINED OUTER 536CIRCULATION...THE INNER CORE HAS NOT CONSOLIDATED AND THERE ARE 537STILL MULTIPLE VORTICITY CENTERS ROTATING AROUND THE MEAN CENTER. 538HIGHLIGHTING THE ISSUE ARE DATA FROM NOAA BUOY 42059...WHICH HAS 539REPORTED 25-30 KT SOUTHWESTERLY WINDS AT A POSITION SOUTHWEST OF 540THE LATEST HURRICANE HUNTER AIRCRAFT FIXES...WHICH IN TURN WERE 541SOUTH OF THE CENTER TRACKED IN THE PREVIOUS ADVISORY. THE INITIAL 542POSITION IS A BLEND OF ALL THESE FEATURES. THE INITIAL INTENSITY 543REMAINS 35 KT BASED ON THE HURRICANE HUNTER DATA. 544 545THE SOMEWHAT UNCERTAIN INITIAL MOTION IS 285/14. THE TRACK MODEL 546GUIDANCE IS IN GOOD AGREEMENT THAT ISAAC SHOULD MOVE GENERALLY 547WEST-NORTHWESTWARD FOR THE NEXT 48-72 HR...AND THIS PART OF THE NEW 548FORECAST TRACK IS VERY SIMILAR TO THE PREVIOUS TRACK. AFTER THAT 549TIME...THE GUIDANCE HAS SHIFTED A LITTLE WESTWARD IN RESPONSE TO 550THE GLOBAL MODELS FORECASTING THE WEAKNESS IN THE SUBTROPICAL RIDGE 551TO BE SOMEWHAT FARTHER WEST THAN BEFORE. THE ECMWF IN PARTICULAR 552HAS MADE A SIGNIFICANT SHIFT...SHOWING A WEST-NORTHWESTWARD MOTION 553INTO THE CENTRAL GULF OF MEXICO BY DAY 5. DESPITE THE GENERAL 554WESTWARD SHIFT...THE HWRF AND CANADIAN MODELS STILL CALL FOR ISAAC 555TO MOVE UP THE FLORIDA PENINSULA. THUS... SIGNIFICANT UNCERTAINTY 556REMAINS ABOUT THE THREAT ISAAC POSES TO FLORIDA AND OTHER PORTIONS 557OF THE GULF COAST. THE 96-120 HR POINTS HAVE BEEN SHIFTED A LITTLE 558WESTWARD FROM THE PREVIOUS ADVISORY AND LIE NEAR THE CENTER OF THE 559GUIDANCE ENVELOPE AND THE CONSENSUS MODELS. 560 561IN THE SHORT TERM...THE STRUCTURE OF ISAAC SUGGESTS THAT ONLY SLOW 562STRENGTHENING IS LIKELY. HOWEVER...THE ENVIRONMENTAL CONDITIONS 563ARE FAVORABLE FOR RAPID INTENSIFICATION...WHICH COULD OCCUR IF THE 564CYCLONE DEVELOPS A WELL-DEFINED INNER CORE. WHILE THE OFFICIAL 565FORECAST NO LONGER SHOWS IT...ISAAC COULD REACH HURRICANE INTENSITY 566ABOUT THE TIME IT MAKES LANDFALL IN HISPANIOLA BETWEEN 24-36 HR. 567AFTER THAT...PASSAGE OVER HISPANIOLA AND CUBA SHOULD CAUSE SOME 568WEAKENING. THE INTENSITY FORECAST SHOWS STRENGTHENING OVER THE GULF 569OF MEXICO...AND THE CURRENT 120 HR INTENSITY COULD BE CONSERVATIVE 570IF THE GLOBAL MODEL UPPER-LEVEL WIND FORECASTS VERIFY. THE NEW 571INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND REMAINS 572STRONGER THAN THE INTENSITY CONSENSUS. 573 574THE NOAA G-IV JET AND AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT 575ARE CURRENTLY CONDUCTING A SYNOPTIC SURVEILLANCE MISSION AROUND 576ISAAC. THE DATA WILL BE AVAILABLE FOR THE 0000 UTC MODEL RUNS. 577 578 579FORECAST POSITIONS AND MAX WINDS 580 581INIT 23/2100Z 16.0N 67.1W 35 KT 40 MPH 582 12H 24/0600Z 16.6N 69.0W 40 KT 45 MPH 583 24H 24/1800Z 17.5N 71.5W 50 KT 60 MPH 584 36H 25/0600Z 18.9N 74.0W 60 KT 70 MPH 585 48H 25/1800Z 20.3N 76.2W 55 KT 65 MPH...INLAND 586 72H 26/1800Z 23.0N 80.0W 50 KT 60 MPH...OVER WATER 587 96H 27/1800Z 25.5N 83.0W 65 KT 75 MPH 588120H 28/1800Z 28.5N 85.5W 75 KT 85 MPH 589 590$$ 591FORECASTER BEVEN 592 593 594WTNT44 KNHC 240250 595TCDAT4 596 597TROPICAL STORM ISAAC DISCUSSION NUMBER 12 598NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 5991100 PM AST THU AUG 23 2012 600 601OBSERVATIONS FROM A NOAA HURRICANE HUNTER AIRCRAFT SUGGEST THAT 602ISAAC HAS STRENGTHENED ONLY SLIGHTLY THIS EVENING. FLIGHT-LEVEL 603AND SFMR-OBSERVED SURFACE WINDS FROM THE AIRCRAFT SUGGEST THAT THE 604CURRENT INTENSITY IS NEAR 40 KT. THE STORM CONTINUES TO HAVE 605FAIRLY STRONG UPPER-LEVEL OUTFLOW AND...IF THE INNER CORE BECOMES 606BETTER DEFINED...HAS AN OPPORTUNITY TO STRENGTHEN AS LONG AS IT 607REMAINS OVER WATER. HOWEVER...THE CENTER OF THE STORM IS FORECAST 608TO MOVE OVER SOUTHWESTERN HISPANIOLA IN 12 HOURS OR SO...AND THIS 609WOULD HALT ANY INTENSIFICATION. A LITTLE LATER ON...LAND 610INTERACTIONS WITH EASTERN CUBA WOULD ALSO INHIBIT INTENSIFICATION 611OR CAUSE WEAKENING. ISAAC WILL LIKELY RESTRENGTHEN WHEN IT MOVES 612OVER THE STRAITS OF FLORIDA AND THE EASTERN GULF OF MEXICO IN THE 613LATTER PART OF THE FORECAST PERIOD. HOWEVER IT SHOULD BE NOTED 614THAT THERE IS SIGNIFICANT UNCERTAINTY IN TROPICAL CYCLONE INTENSITY 615PREDICTIONS AT 3-5 DAYS. 616 617THE INITIAL MOTION ESTIMATE IS 290/16. A MID-TROPOSPHERIC TROUGH 618OVER THE SOUTHEASTERN U.S. IS CAUSING A BREAK IN THE SUBTROPICAL 619RIDGE. IN RESPONSE TO THIS...ISAAC SHOULD TURN TOWARD A MORE 620NORTHWESTWARD HEADING OVER THE NEXT FEW DAYS. THE MODEL CONSENSUS 621HAS SHIFTED A BIT TO THE RIGHT DURING THE FIRST HALF OF THE FORECAST 622PERIOD...PRIMARILY DUE TO AN EASTWARD SHIFT OF THE LATEST GFS 623TRACK. THE OFFICIAL FORECAST IS NUDGED A BIT TO THE RIGHT OF 624THE PREVIOUS ONE AND IS SOMEWHAT FASTER BASED ON THE LATEST MODEL 625GUIDANCE. 626 627THE INITIAL AND FORECAST WIND RADII HAVE BEEN EXPANDED BASED ON BUOY 628AND SHIP DATA. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK 629BECAUSE OF FORECAST UNCERTAINTIES AND THE FACT THAT ISAAC HAS A 630LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. 631 632A SYNOPTIC SURVEILLANCE MISSION BY THE NOAA G-IV JET AIRCRAFT HAS 633BEEN CONDUCTED TO COLLECT ATMOSPHERIC OBSERVATIONS IN THE 634LARGE-SCALE ENVIRONMENT OF ISAAC. THESE DATA WILL BE ASSIMILATED 635INTO THE 0000 UTC RUNS OF THE GLOBAL MODELS...AND SHOULD IMPROVE 636THE ACCURACY OF THEIR FORECASTS FOR THE NEXT ADVISORY CYCLE. 637 638FORECAST POSITIONS AND MAX WINDS 639 640INIT 24/0300Z 16.7N 68.7W 40 KT 45 MPH 641 12H 24/1200Z 17.5N 70.7W 55 KT 65 MPH 642 24H 25/0000Z 18.8N 73.1W 45 KT 50 MPH 643 36H 25/1200Z 20.2N 75.4W 45 KT 50 MPH...INLAND 644 48H 26/0000Z 21.8N 77.7W 45 KT 50 MPH...INLAND 645 72H 27/0000Z 24.8N 82.0W 55 KT 65 MPH...OVER WATER 646 96H 28/0000Z 27.5N 85.5W 70 KT 80 MPH 647120H 29/0000Z 30.0N 88.0W 80 KT 90 MPH 648 649$$ 650FORECASTER PASCH 651 652 653WTNT44 KNHC 240859 654TCDAT4 655 656TROPICAL STORM ISAAC DISCUSSION NUMBER 13 657NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 658500 AM EDT FRI AUG 24 2012 659 660DATA FROM THE HURRICANE HUNTER AIRCRAFT INDICATE THAT ISAAC REMAINS 661POORLY ORGANIZED. WHILE THE 850-MB FLIGHT LEVEL CENTER WAS WELL 662SOUTH OF THE PREVIOUSLY ESTIMATED SURFACE CENTER LOCATION... 663DROPSONDE DATA SUGGEST THAT THE SURFACE CENTER REMAINS FARTHER 664NORTH. FLIGHT LEVEL AND SFMR WINDS SUPPORT MAINTAINING THE 665INTENSITY AT 40 KT FOR THIS ADVISORY...WHILE THE AIRCRAFT FOUND A 666MINIMUM PRESSURE OF 1000 MB. GIVEN THE CURRENT LACK OF ORGANIZATION 667OF THE INNER CORE...ONLY LIMITED STRENGTHENING IS FORECAST BEFORE 668THE CYCLONE BEGINS TO INTERACT WITH HISPANIOLA IN THE NEXT 24 669HOURS. AFTER THAT TIME LITTLE CHANGE IS FORECAST AS ISAAC INTERACTS 670WITH PORTIONS OF CUBA. LATER IN THE PERIOD...ISAAC SHOULD HAVE AN 671OPPORTUNITY TO STRENGTHEN OVER THE STRAITS OF FLORIDA AND THE GULF 672OF MEXICO...AND THE NHC FORECAST IS CLOSE TO THE LGEM MODEL AT DAYS 6734 AND 5. IT SHOULD BE NOTED THAT THERE IS SIGNIFICANT UNCERTAINTY 674IN TROPICAL CYCLONE INTENSITY PREDICTIONS AT 3 TO 5 DAYS. 675 676THE LONG TERM INITIAL MOTION ESTIMATE IS A HIGHLY UNCERTAIN 677275/13...AS THE INITIAL POSITION ESTIMATE IS BASED ON A BLEND OF 678RECENT FIXES AND CONTINUITY. THE TRACK MODEL GUIDANCE CONTINUES TO 679BE IN GENERALLY GOOD AGREEMENT ON THE RESUMPTION OF A WEST- 680NORTHWESTWARD AND THEN NORTHWESTWARD MOTION IN THE NEXT 24 HOURS AS 681THE SUBTROPICAL RIDGE NORTH OF ISAAC WEAKENS. THIS GENERAL MOTION 682SHOULD CONTINUE THROUGH DAY 4...WHEN A TURN MORE TOWARD THE NORTH 683IS SHOWN AS A SHORTWAVE TROUGH AMPLIFIES OVER THE MISSISSIPPI 684VALLEY. LATE IN THE PERIOD THE TRACK MODEL GUIDANCE IS IN BETTER 685AGREEMENT ON THIS SCENARIO...AS THE ECMWF HAS TRENDED EASTWARD 686TOWARD THE REST OF THE MODELS THIS CYCLE. THE NEW NHC FORECAST HAS 687BEEN ADJUSTED ABOUT A DEGREE SOUTHWARD IN THE FIRST 12 HOURS DUE TO 688THE INITIAL POSITION AND MOTION...AND IS THEN BLENDED BACK TOWARD 689THE PREVIOUS TRACK BY 48 HOURS. AFTER THAT TIME...THE NHC FORECAST 690IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ONE...AND IS BETWEEN THE 691ECMWF ON THE LEFT AND THE GFS AND TVCA CONSENSUS ON THE RIGHT. 692 693IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO UNCERTAINTIES 694IN THE INITIAL LOCATION AND THE TRACK FORECAST...AND THE FACT THAT 695ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED 696WITH IT. 697 698FORECAST POSITIONS AND MAX WINDS 699 700INIT 24/0900Z 16.1N 70.0W 40 KT 45 MPH 701 12H 24/1800Z 17.0N 71.9W 50 KT 60 MPH 702 24H 25/0600Z 18.8N 74.1W 45 KT 50 MPH 703 36H 25/1800Z 20.6N 76.7W 45 KT 50 MPH...INLAND 704 48H 26/0600Z 22.4N 78.9W 45 KT 50 MPH...OVER WATER 705 72H 27/0600Z 25.0N 82.5W 55 KT 65 MPH 706 96H 28/0600Z 28.0N 86.0W 65 KT 75 MPH 707120H 29/0600Z 30.5N 87.5W 75 KT 85 MPH...INLAND 708 709$$ 710FORECASTER BRENNAN 711 712 713WTNT44 KNHC 241455 714TCDAT4 715 716TROPICAL STORM ISAAC DISCUSSION NUMBER 14 717NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 7181100 AM EDT FRI AUG 24 2012 719 720RECONNAISSANCE AIRCRAFT DATA AND SATELLITE IMAGERY INDICATE THAT 721ISAAC HAS BECOME BETTER ORGANIZED DURING THE PAST SEVERAL HOURS. 722WHILE THE CIRCULATION CENTER REMAINS ELONGATED EAST-TO-WEST WITH 723MULTIPLE EMBEDDED VORTICITY MAXIMA...THE LARGE CENTRAL AREA OF 724LIGHT WINDS HAS SHRUNK AS THE STRONGEST WINDS MOVE CLOSER TO THE 725CENTER. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT REPORTED 72666 KT FLIGHT-LEVEL WINDS AT 850 MB NORTHEAST OF THE CENTER...ALONG 727WITH SFMR BIAS-CORRECTED WIND ESTIMATES NEAR 50 KT. BASED ON THESE 728DATA...THE INITIAL INTENSITY IS INCREASED TO 50 KT. 729 730THE 12Z POSITION USED A MEAN CENTER...WHICH RESULTED IN A SOUTHWARD 731ADJUSTMENT. SINCE THEN...ISAAC APPEARS TO HAVE ACQUIRED A STRONGER 732NORTHWARD COMPONENT OF MOTION...AND THE INITIAL MOTION IS A 733SOMEWHAT UNCERTAIN 295/12. THE TRACK MODEL GUIDANCE IS IN GOOD 734AGREEMENT THAT ISAAC SHOULD MOVED NORTHWESTWARD FOR THE NEXT 72 735HR...STEERED BY THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC 736TOWARD A WEAKNESS IN THE RIDGE OVER THE SOUTHEASTERN UNITED STATES. 737THIS PART OF THE NEW FORECAST TRACK IS SHIFTED A LITTLE TO THE LEFT 738OF THE PREVIOUS TRACK BASED ON THE INITIAL POSITION...AND LIES NEAR 739THE CONSENSUS MODELS. AFTER 72 HR...THE SPREAD OF THE TRACK 740GUIDANCE INCREASES DUE TO MODEL DISAGREEMENT ON THE EVOLUTION OF A 741TROUGH OVER THE EASTERN UNITED STATES. THE ECMWF KEEPS MORE RIDGE 742BETWEEN ISAAC AND THE TROUGH...WHICH RESULTS IN A NORTHWESTWARD 743MOTION THROUGH DAY 5. THE GFS HAS A STRONGER TROUGH...WHICH 744RESULTS IN A MORE NORTHWARD MOTION. THE GUIDANCE ENVELOPE HAS 745SHIFTED A LITTLE EASTWARD AFTER 72 HR...AND THUS THE LATTER PORTION 746OF THE NEW FORECAST TRACK IS ALSO ADJUSTED EASTWARD. 747 748WHILE THE ORGANIZATION HAS IMPROVED...THE STRUCTURE OF ISAAC STILL 749DOES NOT FAVOR RAPID INTENSIFICATION DESPITE A VERY FAVORABLE 750UPPER-LEVEL WIND PATTERN. THE EARLY PART OF THE INTENSITY FORECAST 751SHOWS A LITTLE MORE STRENGTHENING THAN EARLIER...AND IT IS POSSIBLE 752THAT ISAAC COULD BE NEAR HURRICANE STRENGTH WHEN IT REACHES 753HISPANIOLA. LAND INTERACTION WILL LIMIT THE INTENSITY FROM 24-48 754HR...AND THIS PART OF THE FORECAST MAY NEED SOME ADJUSTMENT AFTER 755IT IS SEEN WHAT STRUCTURE ISAAC HAS AFTER CROSSING HISPANIOLA. 756ISAAC SHOULD STRENGTHEN OVER THE GULF OF MEXICO...WITH THE FORECAST 757SHOWING THE CYCLONE BECOMING A HURRICANE BEFORE REACHING THE 758NORTHERN GULF COAST. 759 760IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO THE 761UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE 762AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. 763 764 765FORECAST POSITIONS AND MAX WINDS 766 767INIT 24/1500Z 16.3N 70.8W 50 KT 60 MPH 768 12H 25/0000Z 17.4N 72.6W 55 KT 65 MPH 769 24H 25/1200Z 19.2N 75.1W 55 KT 65 MPH 770 36H 26/0000Z 20.9N 77.6W 50 KT 60 MPH...INLAND 771 48H 26/1200Z 22.3N 79.5W 45 KT 50 MPH...INLAND 772 72H 27/1200Z 25.0N 83.0W 55 KT 65 MPH...OVER WATER 773 96H 28/1200Z 28.0N 85.5W 65 KT 75 MPH 774120H 29/1200Z 31.0N 86.5W 70 KT 80 MPH...INLAND 775 776$$ 777FORECASTER BEVEN 778 779 780WTNT44 KNHC 242055 781TCDAT4 782 783TROPICAL STORM ISAAC DISCUSSION NUMBER 15 784NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 785500 PM EDT FRI AUG 24 2012 786 787RECONNAISSANCE AIRCRAFT DATA INDICATE THAT THE CIRCULATION OF ISAAC 788HAS BECOME BETTER ORGANIZED THIS AFTERNOON...WITH A WELL-DEFINED 789AND MORE CIRCULAR INNER CIRCULATION. THE MAXIMUM 850 MB 790FLIGHT-LEVEL WINDS HAVE BEEN 70 KT...THE MAXIMUM RELIABLE SFMR 791SURFACE WIND ESTIMATE HAS BEEN 55 KT...AND THE MINIMUM REPORTED 792PRESSURE HAS BEEN 994 MB. BASED ON THESE DATA...THE INITIAL 793INTENSITY IS INCREASED TO 55 KT. ONE SIGN OF ONGOING ORGANIZATION 794ISSUES...HOWEVER...IS THE LACK OF PERSISTENCE OF THE INNER CORE 795CONVECTION...WHICH HAS WANED OVER THE PAST FEW HOURS. 796 797ISAAC HAS MADE ITS EXPECTED TURN TOWARD THE NORTHWEST AND THE 798INITIAL MOTION IS NOW 315/14. DURING THE FIRST 48-60 HR...THE 799TRACK GUIDANCE MADE AN EASTWARD SHIFT SINCE THE LAST ADVISORY. 800THIS WAS LED BY THE GFS...WHICH CHANGED TO A TRACK INTO THE 801SOUTHEASTERN GULF OF MEXICO TO LANDFALL IN SOUTHEASTERN FLORIDA. 802THE ECMWF AND UKMET ARE NOW ON THE LEFT EDGE OF THE GUIDANCE... 803SHOWING A TRACK ALONG THE NORTH COAST OF CUBA. THIS PART OF 804THE FORECAST TRACK IS SHIFTED EASTWARD BUT STILL LIES A LITTLE TO 805THE LEFT OF THE CENTER OF THE GUIDANCE ENVELOPE AND THE CONSENSUS 806MODELS. THERE REMAINS A SPREAD IN THE MODEL GUIDANCE AFTER 48 807HR. THE GFS-BASED GUIDANCE SHOWS A NORTHEASTWARD MOTION AFTER 808LANDFALL ON THE NORTHERN GULF COAST...WHILE THE UKMET AND ECMWF 809SHOW A NORTHWARD MOTION. THE LATTER PART OF THE FORECAST TRACK IS 810SHIFTED EASTWARD CLOSE TO THE CONSENSUS MODELS. 811 812THE MAIN CONVECTIVE BAND AND STRONGEST WINDS NORTHEAST OF THE CENTER 813ARE MOVING INLAND AT THIS TIME. BASED ON THIS AND THE CURRENT LACK 814OF CONVECTION NEAR THE CENTER...LITTLE CHANGE IN STRENGTH IS 815EXPECTED BEFORE LANDFALL. THE INTENSITY FROM 12-48 HR WILL BE 816DETERMINED BY THE AMOUNT OF LAND INTERACTION. THE CURRENT FORECAST 817IS BASED ON THE PREMISE THAT ISAAC WILL REMAIN OVER LAND LONG 818ENOUGH TO ALLOW GRADUAL WEAKENING. HOWEVER...ANY CHANGE IN THE 819TRACK THAT ALLOWS IT TO REMAIN OVER WATER FOR A LONGER TIME COULD 820ALLOW IT TO BE STRONGER THAN FORECAST. AFTER 48 HR...THE 821ENVIRONMENTAL CONDITIONS APPEAR GENERALLY FAVORABLE FOR ISAAC TO 822STRENGTHEN INTO A HURRICANE OVER THE GULF OF MEXICO...AND THE 823INTENSITY FORECAST REFLECTS THIS. CONVERSELY...A LONGER TRACK OVER 824LAND MAY DISRUPT ISAAC ENOUGH TO BE UNABLE TO TAKE ADVANTAGE OF 825THESE FAVORABLE CONDITIONS. 826 827IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO THE 828UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE 829AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. THE TROPICAL 830STORM WATCH FOR SOUTH FLORIDA AND THE FLORIDA KEYS MAY HAVE TO BE 831UPGRADED TO A HURRICANE WATCH IF THE INTENSITY FORECAST IS REVISED 832UPWARD. 833 834FORECAST POSITIONS AND MAX WINDS 835 836INIT 24/2100Z 17.2N 71.9W 55 KT 65 MPH 837 12H 25/0600Z 18.7N 73.6W 50 KT 60 MPH 838 24H 25/1800Z 20.7N 76.2W 50 KT 60 MPH...INLAND 839 36H 26/0600Z 22.4N 78.6W 45 KT 50 MPH...NEAR COAST OF CUBA 840 48H 26/1800Z 23.9N 80.7W 55 KT 65 MPH...OVER WATER 841 72H 27/1800Z 26.5N 84.0W 65 KT 75 MPH 842 96H 28/1800Z 29.5N 86.0W 75 KT 85 MPH 843120H 29/1800Z 32.0N 86.0W 45 KT 50 MPH...INLAND 844 845$$ 846FORECASTER BEVEN 847 848 849WTNT44 KNHC 250319 850TCDAT4 851 852TROPICAL STORM ISAAC DISCUSSION NUMBER 16 853NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 8541100 PM EDT FRI AUG 24 2012 855 856SATELLITE IMAGERY AND RECONNAISSANCE AIRCRAFT DATA INDICATE THAT THE 857CIRCULATION AND CONVECTIVE ORGANIZATION OF ISAAC HAS CONTINUED TO 858IMPROVE SINCE THE PREVIOUS ADVISORY. INFRARED AND MICROWAVE 859SATELLITE IMAGERY SUGGEST THAT AN EYE IS FORMING...AND THIS IS THE 860BASIS FOR INCREASING THE INTENSITY TO 60 KT. 861 862THE INITIAL MOTION ESTIMATE IS 315/12 BASED ON RECON AND MICROWAVE 863FIXES. ALTHOUGH THE TRACK FORCAST WAS ADJUSTED SLIGHTLY TO THE 864RIGHT THROUGH 48 HOURS...NO OTHER SIGNIFICANT CHANGES WERE MADE TO 865THE PREVIOUS ADVISORY TRACK. RECENT UPPER-AIR DATA AND NOAA G-IV 866AIRCRAFT DROPSONDE DATA INDICATE THE TROUGH THAT HAS CREATED THE 867BREAK IN THE SUBTROPICAL RIDGE ACROSS FLORIDA HAS SHIFTED TO A 868POSITION JUST EAST OF THE FLORIDA PENINSULA. THE 18Z GFS MODEL... 869WHICH SHIFTED TO THE RIGHT OF ITS 12Z TRACK...CAPTURED THIS FARTHER 870EAST POSITION...WHEREAS THE 18Z UKMET AND 12Z ECMWF KEPT THE TROUGH 871ACROSS THE WESTERN FLORIDA PENINSULA VALID AT 00Z THIS EVENING. 872BASED ON THE GFS VERIFYING BETTER THAN THE OTHER MODELS AT 00Z THIS 873EVENING...THE NHC TRACK HAS BEEN SHIFTED A LITTLE TO THE RIGHT. 874AFTER 48 HOURS...THE RIDGE IS EXPECTED TO BUILD BACK WESTWARD 875ACROSS FLORIDA AND KEEPING ISAAC ON A MOSTLY NORTHWESTWARD HEADING 876ACROSS THE EASTERN AND NORTH-CENTRAL GULF MEXICO. THE OFFICIAL 877FORECAST TRACK IS CLOSE TO THE CONSENSUS MODELS TVCA AND TV15 878THROUGH 48 HOURS...AND THEN IS A LITTLE TO THE RIGHT OF THOSE 879MODELS AFTER THAT. 880 881WITH THE INNER CORE CONVECTION IMPROVING...THERE IS STILL THE 882POSSIBILITY THAT ISAAC COULD REACH HURRICANE INTENSITY BEFORE 883REACHING HAITI TONIGHT. THE INTENSITY FROM 12-24 HOURS WILL BE 884DETERMINED BY THE AMOUNT OF LAND INTERACTION WITH HAITI AND EASTERN 885CUBA. AFTER THAT...THE SLIGHT EASTWARD SHIFT IN THE FORECAST TRACK 886IS ENOUGH TO PLACE ISAAC OVER WATER LONGER THAN WHAT WAS INDICATED 887IN THE PREVIOUS INTENSITY FORECAST REQUIRED AN INCREASE IN THE 888INTENSITY FORECAST. THE EASTWARD TRACK SHIFT AND A LARGER INITIAL 889AND FORECAST WIND FIELD TO THE NORTH ARE WHAT NECESSITATED THE 890CHANGES IN THE WATCHES AND WARNINGS FOR FLORIDA. 891 892IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO THE 893UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE 894AREA OF TROPICAL-STORM-FORCE WINDS ASSOCIATED WITH IT. 895 896FORECAST POSITIONS AND MAX WINDS 897 898INIT 25/0300Z 17.7N 72.5W 60 KT 70 MPH 899 12H 25/1200Z 19.4N 74.1W 50 KT 60 MPH 900 24H 26/0000Z 21.7N 76.7W 50 KT 60 MPH 901 36H 26/1200Z 23.4N 79.4W 55 KT 65 MPH 902 48H 27/0000Z 24.9N 81.6W 60 KT 70 MPH 903 72H 28/0000Z 27.1N 84.6W 70 KT 80 MPH 904 96H 29/0000Z 30.0N 86.5W 80 KT 90 MPH 905120H 30/0000Z 32.5N 86.5W 40 KT 45 MPH...INLAND 906 907$$ 908FORECASTER STEWART 909 910 911WTNT44 KNHC 250859 912TCDAT4 913 914TROPICAL STORM ISAAC DISCUSSION NUMBER 17 915NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 916500 AM EDT SAT AUG 25 2012 917 918THE CIRCULATION OF ISAAC HAS REMAINED RELATIVELY INTACT AFTER MOVING 919ACROSS THE SOUTHWESTERN PENINSULA OF HAITI OVERNIGHT. BEFORE THE 920CENTER MOVED INLAND...HURRICANE HUNTER AIRCRAFT DATA SUGGESTED THAT 921THE CYCLONE HAD PEAK WINDS OF ABOUT 55 KT. ASSUMING THE CYCLONE 922WEAKENED A LITTLE AFTER ENCOUNTERING THE HIGH TERRAIN...THE INITIAL 923INTENSITY IS LOWERED TO 50 KT FOR THIS ADVISORY. 924 925THE INITIAL MOTION ESTIMATE IS 320/12. AS A MID-LEVEL TROUGH LIFTS 926OUT OF THE SOUTHEASTERN UNITED STATES...ISAAC WILL MOVE GENERALLY 927WEST-NORTHWESTWARD AROUND THE WEST SIDE OF THE SUBTROPICAL RIDGE 928FOR THE NEXT THREE DAYS OR SO...AND THEN TURN NORTHWARD LATE IN THE 929PERIOD AS A SHORTWAVE TROUGH AMPLIFIES OVER THE EASTERN UNITED 930STATES. THERE HAS BEEN LITTLE CHANGE TO THE NHC FORECAST THIS 931CYCLE...AND THE NEW TRACK FORECAST IS CLOSE TO THE MIDDLE OF THE 932GUIDANCE ENVELOPE AND LIES CLOSE TO THE GFS AND THE TVCA 933MULTI-MODEL CONSENSUS THROUGH 96 HOURS. BY DAY 5 THERE IS SOME 934DISAGREEMENT AS TO WHETHER ISAAC WILL TURN NORTHEASTWARD AHEAD OF 935THE SHORTWAVE TROUGH AS SHOWN BY THE GFS...UKMET...AND THE GFDL OR 936BE LEFT BEHIND AS SHOWN BY THE ECMWF AND HWRF. THE NHC DAY 5 POINT 937IS BETWEEN THE TWO CAMPS SHOWING A SLOW NORTHWARD MOTION. 938 939GIVEN THAT THE CYCLONE HAS FARED RATHER WELL AFTER MOVING ACROSS 940HAITI...AND THAT THE TRACK FORECAST HAS ONLY MINIMAL INTERACTION 941WITH CUBA...THE INTENSITY FORECAST AFTER 12 HOURS HAS BEEN ADJUSTED 942UPWARD FOLLOWING THE TREND OF THE LATEST INTENSITY GUIDANCE. ISAAC 943IS EXPECTED TO BECOME A HURRICANE IN ABOUT 36 HOURS...WITH 944ADDITIONAL INTENSIFICATION EXPECTED AS THE CYCLONE MOVES INTO THE 945EASTERN GULF OF MEXICO IN A FAVORABLE ENVIRONMENT. THE NEW NHC 946INTENSITY FORECAST IS CLOSE TO THE INTENSITY CONSENSUS AIDS THROUGH 94772 HOURS AND FOLLOWS A BLEND OF THE DECAY SHIPS AND LGEM AFTERWARD. 948 949THE NEW NHC FORECAST NECESSITATES THE ISSUANCE OF A HURRICANE 950WARNING FOR THE FLORIDA KEYS AND A PORTION OF THE SOUTHWEST COAST 951OF FLORIDA AT THIS TIME. 952 953IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF ISAAC DUE TO THE 954UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE 955AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. 956 957FORECAST POSITIONS AND MAX WINDS 958 959INIT 25/0900Z 19.0N 73.3W 50 KT 60 MPH 960 12H 25/1800Z 20.4N 75.0W 50 KT 60 MPH...INLAND 961 24H 26/0600Z 22.2N 77.6W 55 KT 65 MPH...OVER WATER 962 36H 26/1800Z 23.8N 80.0W 65 KT 75 MPH 963 48H 27/0600Z 25.0N 81.8W 70 KT 80 MPH 964 72H 28/0600Z 27.7N 84.9W 80 KT 90 MPH 965 96H 29/0600Z 30.5N 86.0W 70 KT 80 MPH...INLAND 966120H 30/0600Z 32.5N 86.0W 35 KT 40 MPH...INLAND 967 968$$ 969FORECASTER BRENNAN 970 971 972WTNT44 KNHC 251502 973TCDAT4 974 975TROPICAL STORM ISAAC DISCUSSION NUMBER 18 976NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 9771100 AM EDT SAT AUG 25 2012 978 979ISAAC HAS BEEN SOMEWHAT DISRUPTED BY ITS PASSAGE ACROSS HAITI. THE 980LAST REPORT FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT 981SHOWED THAT THE CENTER PRESSURE HAD RISEN TO 998 MB...AND THAT THE 982STRONGEST FLIGHT-LEVEL WINDS WERE 60-70 N MI FROM THE CENTER. THESE 983WINDS SUPPORT AN INITIAL INTENSITY OF 50 KT. THE CONVECTIVE 984PATTERN IS DISORGANIZED...WITH LARGE CONVECTIVE BANDS SOUTH OF 985HISPANIOLA AND LITTLE CONVECTION CURRENTLY NEAR THE CENTER. IT 986SHOULD BE NOTED THAT ISAAC IS AT THE EASTERN END OF A LARGE AND 987ELONGATED LOW PRESSURE SYSTEM OVER THE NORTHWESTERN CARIBBEAN 988SEA...WHICH IS CREATING A LARGE AREA OF STRONG EASTERLY LOW-LEVEL 989WINDS WELL TO THE NORTHWEST OF THE CENTER. 990 991THE LOW-LEVEL CENTER HAS JOGGED WESTWARD DURING THE PAST FEW 992HOURS...AND THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 315/15. IN 993THE SHORT-TERM...A MID/UPPER-LEVEL TROUGH OVER THE EASTERN UNITED 994STATES IS LIFTING OUT TO THE NORTHEAST AS A UPPER-LEVEL LOW MOVES 995SOUTHWARD ACROSS THE CENTRAL GULF OF MEXICO. THIS EVOLUTION... 996COMBINED WITH THE LOW-LEVEL RIDGE NORTH OF ISAAC...SHOULD STEER THE 997CYCLONE GENERALLY NORTHWESTWARD NEAR THE NORTH COAST OF CUBA AND THE 998FLORIDA KEYS DURING THE NEXT 48 HR AS INDICATED BY THE TIGHTLY- 999CLUSTERED MODEL GUIDANCE. AFTER THAT...THE CYCLONE IS EXPECTED TO 1000MOVE AROUND THE WESTERN END OF THE SUBTROPICAL RIDGE AND TURN MORE 1001NORTHWARD OVER THE EASTERN GULF OF MEXICO. WHILE THE GUIDANCE 1002GENERALLY AGREES WITH THIS SCENARIO...THERE IS A SPREAD IN 1003POTENTIAL LANDFALL LOCATIONS BETWEEN THE EASTERN FLORIDA PANHANDLE 1004AND SOUTHEASTERN LOUISIANA...WHICH LOWERS CONFIDENCE IN THE FINAL 1005LANDFALL POINT. THE NEW FORECAST TRACK FOLLOWS THE CENTER OF THE 1006GUIDANCE ENVELOPE AND THE CONSENSUS MODELS IN CALLING FOR LANDFALL 1007IN THE WESTERN FLORIDA PANHANDLE BETWEEN 72-96 HR. 1008 1009LITTLE CHANGE IN STRENGTH IS EXPECTED TODAY DUE TO A COMBINATION OF 1010LAND INTERACTION...SOME WESTERLY SHEAR...AND THE CURRENT LACK OF 1011CONVECTION. THE SHEAR IS FORECAST TO DECREASE AS THE CENTER MOVES 1012AWAY FROM LAND...WOULD SHOULD ALLOW FOR STRENGTHENING AFTER 12 HR. 1013THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST 1014THROUGH 48 HR...THEN CALLS FOR A LITTLE MORE STRENGTHENING THAN THE 1015PREVIOUS FORECAST OVER THE NORTHERN GULF. THE CYCLONE SHOULD 1016WEAKEN TO A DEPRESSION AFTER LANDFALL ON THE NORTHERN GULF COAST. 1017 1018THE NEW NHC FORECAST NECESSITATES THE ISSUANCE OF ADDITIONAL 1019TROPICAL STORM WARNINGS AND WATCHES FOR PORTIONS OF THE FLORIDA 1020PENINSULA. 1021 1022IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF ISAAC DUE TO THE 1023UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE 1024AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. 1025 1026FORECAST POSITIONS AND MAX WINDS 1027 1028INIT 25/1500Z 20.1N 74.6W 50 KT 60 MPH 1029 12H 26/0000Z 21.7N 76.4W 50 KT 60 MPH 1030 24H 26/1200Z 23.3N 79.0W 55 KT 65 MPH 1031 36H 27/0000Z 24.7N 81.3W 65 KT 75 MPH 1032 48H 27/1200Z 25.9N 83.1W 75 KT 85 MPH 1033 72H 28/1200Z 28.5N 85.5W 85 KT 100 MPH 1034 96H 29/1200Z 31.5N 86.5W 65 KT 75 MPH...INLAND 1035120H 30/1200Z 33.0N 86.0W 30 KT 35 MPH...INLAND 1036 1037$$ 1038FORECASTER BEVEN 1039 1040 1041WTNT44 KNHC 252102 1042TCDAT4 1043 1044TROPICAL STORM ISAAC DISCUSSION NUMBER 19 1045NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1046500 PM EDT SAT AUG 25 2012 1047 1048THE CENTER OF ISAAC IS CURRENTLY MOVING ALONG THE NORTH COAST OF 1049EASTERN CUBA. THE SATELLITE APPEARANCE IS SOMEWHAT DISORGANIZED... 1050WITH THE MAIN CONVECTIVE MASS 50 N MI OR MORE EAST OF THE LOW-LEVEL 1051CENTER. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS 1052REPORTED 850 MB FLIGHT-LEVEL WINDS OF 56 KT TO THE NORTHEAST OF THE 1053CENTER...WITH RELIABLE-LOOKING SFMR SURFACE WIND DATA NEAR 50 KT. 1054BASED ON THIS...THE INITIAL INTENSITY REMAINS 50 KT. THE CENTRAL 1055PRESSURE OF 997 MB IS BASED ON A COMBINATION OF AIRCRAFT DATA AND 1056CUBAN SURFACE OBSERVATIONS. 1057 1058THE INITIAL MOTION IS NOW 310/18. ISAAC IS CURRENTLY PART OF A 1059LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM COVERING THE NORTHWESTERN 1060CARIBBEAN SEA AND THE ADJACENT LAND AND OCEAN AREAS. THIS LOW 1061PRESSURE AREA HAS A SECOND VORTICITY CENTER BETWEEN JAMAICA AND THE 1062CAYMAN ISLANDS...AND FOR THE NEXT 24-36 HR ISAAC AND THIS CENTER 1063WILL LIKELY ROTATE AROUND EACH OTHER. BASED ON THIS EXPECTATION... 1064THE FORECAST TRACK SHOWS ISAAC MOVING NORTHWESTWARD FOR 12 HR OR 1065SO...FOLLOWED BY A TURN TOWARD THE WEST-NORTHWEST. IT IS POSSIBLE 1066THE STORM COULD MAKE A SHARPER TURN THAN FORECAST...AS THE UKMET IS 1067SHOWING AN ALMOST DUE WEST MOTION BETWEEN THE FLORIDA KEYS AND CUBA 1068NEAR THE 36 HR POINT. THE EARLY PART OF THE FORECAST TRACK IS 1069SHIFTED A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST...BUT STILL 1070LIES TO THE RIGHT OF THE CONSENSUS MODELS AND THE BULK OF THE 1071DYNAMICAL MODELS. AFTER 36 HR...ISAAC SHOULD BREAK FREE OF OR 1072ABSORB THE REST OF THE LOW...WITH THE SUBTROPICAL RIDGE TO THE EAST 1073BECOMING THE DOMINANT STEERING INFLUENCE. THIS SHOULD ALLOW THE 1074STORM TO GRADUALLY TURN TOWARD THE NORTHWEST AND NORTH OVER THE 1075EASTERN AND NORTHERN GULF OF MEXICO...WITH AN EVENTUAL LANDFALL 1076ALONG THE NORTHERN GULF COAST IN 72-96 HR. WHERE THIS MIGHT OCCUR 1077IS STILL RATHER UNCERTAIN...WITH THE TRACK GUIDANCE SPREAD BETWEEN 1078SOUTHEASTERN LOUISIANA AND THE CENTRAL FLORIDA PANHANDLE. THIS PART 1079OF THE TRACK FORECAST LIES IN THE CENTER OF THE GUIDANCE ENVELOPE 1080NEAR THE CONSENSUS MODELS AND IS SIMILAR TO THE PREVIOUS FORECAST. 1081 1082A COMBINATION OF LIGHT WESTERLY VERTICAL WIND SHEAR AND LAND 1083INTERACTION SHOULD AT LEAST SLOW INTENSIFICATION FOR THE NEXT 12 1084HR. AFTER THAT...THE SHEAR SHOULD DIMINISH WHILE THE CYCLONE 1085REACHES OPEN WATER. THIS SHOULD ALLOW ISAAC TO GRADUALLY STRENGTHEN 1086INTO A HURRICANE NEAR THE FLORIDA KEYS OR OVER THE SOUTHEASTERN 1087GULF OF MEXICO. THE NEW INTENSITY FORECAST IS SIMILAR TO THE 1088PREVIOUS FORECAST AND IS NEAR OR A LITTLE ABOVE THE INTENSITY 1089CONSENSUS. IT SHOULD BE NOTED THAT THE GLOBAL MODELS ARE 1090FORECASTING A VERY FAVORABLE PATTERN OF UPPER-LEVEL WINDS OVER THE 1091NORTHERN GULF OF MEXICO BY 72 HR. SHOULD THIS VERIFY AND SHOULD 1092ISAAC ESTABLISH AN INNER CORE...THE CYCLONE COULD BE SIGNIFICANTLY 1093STRONGER THAN CURRENTLY FORECAST. 1094 1095IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF ISAAC DUE TO THE 1096UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE 1097AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. 1098 1099 1100FORECAST POSITIONS AND MAX WINDS 1101 1102INIT 25/2100Z 21.3N 76.0W 50 KT 60 MPH 1103 12H 26/0600Z 22.6N 78.0W 55 KT 65 MPH 1104 24H 26/1800Z 24.1N 80.6W 60 KT 70 MPH 1105 36H 27/0600Z 25.2N 82.7W 65 KT 75 MPH 1106 48H 27/1800Z 26.5N 84.3W 75 KT 85 MPH 1107 72H 28/1800Z 29.0N 86.0W 85 KT 100 MPH 1108 96H 29/1800Z 31.5N 86.0W 55 KT 65 MPH...INLAND 1109120H 30/1800Z 33.5N 85.5W 25 KT 30 MPH...INLAND 1110 1111$$ 1112FORECASTER BEVEN 1113 1114 1115WTNT44 KNHC 260244 1116TCDAT4 1117 1118TROPICAL STORM ISAAC DISCUSSION NUMBER 20 1119NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 11201100 PM EDT SAT AUG 25 2012 1121 1122SATELLITE AND RADAR DATA FROM CUBA SHOW THAT ISAAC IS MOVING 1123PARALLEL TO...BUT OFFSHORE OF...THE NORTHERN COAST OF CUBA. 1124THE HURRICANE HUNTER AIRCRAFT DID NOT FIND ANY STRONGER WINDS 1125DURING THE LATTER PORTION OF THE FLIGHT AND THE INITIAL WIND 1126SPEED REMAINS 50 KT. HOWEVER...THUNDERSTORM ACTIVITY HAS 1127INCREASED IN A BAND TO THE NORTH AND EAST OF THE CENTER DURING 1128THE PAST FEW HOURS AND ISAAC MAY BE ON THE VERGE OF STRENGTHENING. 1129THE NEXT RECONNAISSANCE FLIGHT IS EXPECTED TO BE IN THE CYCLONE 1130AROUND 0600 UTC. 1131 1132THE INITIAL MOTION ESTIMATE IS 305/15 KT. ISAAC SHOULD CONTINUE ON 1133A WEST-NORTHWESTWARD TO NORTHWESTWARD MOTION DURING THE NEXT 24 1134HOURS OR SO BETWEEN A LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM OVER 1135THE NORTHWESTERN CARIBBEAN SEA AND A MID-LEVEL RIDGE OVER THE 1136WESTERN ATLANTIC. THE MODEL GUIDANCE IS TIGHTLY CLUSTERED DURING 1137THIS TIME AND SHOWS A TRACK OVER THE STRAITS OF FLORIDA AND NEAR OR 1138OVER THE FLORIDA KEYS. IN ABOUT 48 HOURS...ISAAC WILL BE NEARING 1139THE WESTERN PORTION OF THE RIDGE AND SHOULD MOVE IN A GENERAL 1140NORTHWESTWARD HEADING OVER THE EASTERN GULF OF MEXICO...BUT LARGE 1141DIFFERENCES EXIST BETWEEN THE LATEST ECMWF AND GFS MODELS AFTER 1142THAT TIME. THE ECMWF RECURVES ISAAC AHEAD OF A MID-LATITUDE 1143TROUGH OVER THE EASTERN UNITED STATES...WHILE THE GFS SLOWS ISAAC 1144DOWN AS THE TROUGH BYPASSES THE SYSTEM AND THE MODEL THEN TURNS 1145THE CYCLONE WESTWARD TO THE SOUTH OF A DEVELOPING MID- TO 1146UPPER-LEVEL RIDGE. THIS BIFURCATION IS ALSO SEEN IN THE MOST RECENT 1147ECMWF AND GFS ENSEMBLES WITH ABOUT AN EQUAL NUMBER OF MEMBERS 1148SHOWING RECURVATURE VERSUS A CONTINUE NORTHWESTERLY TRACK TOWARD 1149THE NORTHERN GULF COAST. SINCE THE UNCERTAINTY IS LARGE AND EITHER 1150OF THESE SCENARIOS ARE POSSIBLE AT THIS TIME...THE NHC FORECAST IS 1151LIES BETWEEN THEM. THE UPDATED TRACK IS VERY CLOSE TO THE PREVIOUS 1152ADVISORY THROUGH 36 HOURS. AFTER THAT TIME...THE TRACK HAS BEEN 1153ADJUSTED WESTWARD...BUT IT REMAINS EAST OF THE DYNAMICAL MODEL 1154CONSENSUS TO RETAIN SOME CONTINUITY WITH THE PREVIOUS FORECAST. 1155 1156THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO BECOME MORE CONDUCIVE FOR 1157STRENGTHENING DURING THE NEXT COUPLE OF DAYS AS ISAAC MOVES OVER 1158THE WARM WATERS OF THE FLORIDA STRAITS AND EASTERN GULF. STEADY 1159STRENGTHENING IS EXPECTED AND ISAAC IS EXPECTED TO BE AT OR NEAR 1160HURRICANE STRENGTH WHEN THE CENTER REACHES THE FLORIDA KEYS. 1161ADDITIONAL STRENGTHENING IS LIKELY WHILE THE CYCLONE MOVES OVER THE 1162EASTERN GULF OF MEXICO. THE NEW INTENSITY FORECAST IS A LITTLE 1163HIGHER THAN THE PREVIOUS ADVISORY AND IS BETWEEN THE SHIPS/LGEM 1164GUIDANCE AND THE MORE AGGRESSIVE HWRF MODEL. 1165 1166IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK SINCE 1167SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER. SINCE LARGE 1168UNCERTAINTIES REMAIN IN THE EXTENDED PORTION OF THE FORECAST...IT 1169IS TOO EARLY TO DETERMINE EXACTLY WHERE AND WHEN ISAAC WILL MAKE 1170LANDFALL ALONG THE GULF COAST. 1171 1172FORECAST POSITIONS AND MAX WINDS 1173 1174INIT 26/0300Z 22.1N 77.2W 50 KT 60 MPH 1175 12H 26/1200Z 23.4N 79.4W 55 KT 65 MPH 1176 24H 27/0000Z 24.6N 81.8W 65 KT 75 MPH...NEAR FLORIDA KEYS 1177 36H 27/1200Z 25.8N 83.7W 75 KT 85 MPH 1178 48H 28/0000Z 27.2N 85.2W 85 KT 100 MPH 1179 72H 29/0000Z 29.5N 86.5W 90 KT 105 MPH 1180 96H 30/0000Z 31.5N 86.5W 50 KT 60 MPH...INLAND 1181120H 31/0000Z 34.0N 86.0W 25 KT 30 MPH...INLAND 1182 1183$$ 1184FORECASTER BROWN 1185 1186 1187WTNT44 KNHC 260900 1188TCDAT4 1189 1190TROPICAL STORM ISAAC DISCUSSION NUMBER 21 1191NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1192500 AM EDT SUN AUG 26 2012 1193 1194WHILE THE SATELLITE PRESENTATION OF ISAAC REMAINS SOMEWHAT 1195UNIMPRESSIVE...WITH DEEP CONVECTION LIMITED TO A RATHER SMALL AREA 1196NORTH AND EAST OF THE CENTER...AIRCRAFT DATA SUGGEST THAT THE 1197CYCLONE HAS STRENGTHENED A LITTLE OVERNIGHT. PEAK 850-MB 1198FLIGHT-LEVEL WINDS OF 69 KT IN THE NORTHEAST QUADRANT ADJUST TO AN 1199INTENSITY OF 55 KT...WHICH IS THE VALUE FOR THIS ADVISORY. AIRCRAFT 1200DATA INDICATE THAT THE MINIMUM PRESSURE HAS ALSO DROPPED A LITTLE... 1201TO 995 MB. ISAAC STILL APPEARS TO BE BATTLING THE EFFECTS OF SOME 1202LOW- TO MID-LEVEL DRY AIR IN THE WESTERN SIDE OF THE CIRCULATION... 1203AS SEEN IN UPPER-AIR DATA FROM MIAMI AND KEY WEST. ASIDE FROM 1204THIS...HOWEVER...CONDITIONS APPEAR FAVORABLE FOR STEADY 1205INTENSIFICATION AS THE CYCLONE MOVE ACROSS THE FLORIDA STRAITS AND 1206INTO THE EASTERN GULF OF MEXICO. WATERS ALONG THE FORECAST TRACK ARE 1207VERY WARM...AND UPPER-LEVEL WINDS ARE FORECAST BY THE GLOBAL MODELS 1208TO BECOME CONDUCIVE FOR STRENGTHENING. THE NEW NHC FORECAST IS 1209SIMILAR TO THE PREVIOUS ONE...BUT SHOWS A LITTLE SLOWER RATE OF 1210STRENGTHENING FOR THE FIRST COUPLE OF DAYS...TRENDING TOWARD THE 1211LATEST CYCLE OF GUIDANCE. 1212 1213THE INITIAL MOTION ESTIMATE IS 305/16...A LITTLE FASTER THAN BEFORE. 1214AS THE UPPER-LOW TO THE WEST OF ISAAC RETREATS WESTWARD AND THE 1215CLOSED LOW OVER THE MID-ATLANTIC STATES LIFTS NORTHWARD...ISAAC 1216WILL MOVE GENERALLY WEST-NORTHWESTWARD OR NORTHWESTWARD AROUND THE 1217WESTERN PERIPHERY OF THE ATLANTIC SUBTROPICAL RIDGE FOR THE NEXT 48 1218HOURS. BEYOND THAT TIME...THERE IS CONSIDERABLE SPREAD IN THE MODEL 1219GUIDANCE. MOST OF THE MODELS...WITH THE EXCEPTION OF THE UKMET...NO 1220LONGER SHOW ISAAC RECURVING AHEAD OF A SHORTWAVE TROUGH MOVING 1221EASTWARD ACROSS THE EASTERN UNITED STATES. ONE CAMP OF GUIDANCE... 1222INCLUDING THE GFS...HWRF...AND GFS ENSEMBLE MEAN SHOW A 1223NORTHWESTWARD TRACK TOWARD THE CENTRAL GULF COAST AS THE SHORTWAVE 1224BYPASSES ISAAC COMPLETELY. THE ECMWF AND GFDL SHOW HAVE MORE OF A 1225WEAKNESS IN THE RIDGE AND SHOW ISAAC TURNING NORTHWARD TOWARD THE 1226EASTERN GULF COAST. THE NEW NHC FORECAST IS FASTER THAN THE 1227PREVIOUS ONE THROUGH MUCH OF THE PERIOD...BUT IS ALONG THE PREVIOUS 1228TRACK THROUGH 36 HOURS. AFTER THAT TIME...A SIGNIFICANT WESTWARD 1229ADJUSTMENT WAS MADE...AND THE NEW NHC TRACK IS CLOSE TO THE TVCA 1230MULTI-MODEL CONSENSUS AND THE ECMWF...SHOWING A NORTH-NORTHWESTWARD 1231AND NORTHWARD TURN AT DAYS 3 THROUGH 5. GIVEN THE LARGE SPREAD IN 1232THE GUIDANCE...CONFIDENCE IN THE LONG-RANGE TRACK FORECAST IS QUITE 1233LOW...AND IT IS TOO EARLY TO DETERMINE EXACTLY WHERE AND WHEN ISAAC 1234WILL MAKE LANDFALL ALONG THE GULF COAST. FURTHER ADJUSTMENTS TO THE 1235TRACK MAY BE NECESSARY LATER TODAY. 1236 1237THROUGHOUT THE PERIOD...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT 1238FORECAST TRACK SINCE SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE 1239CENTER. 1240 1241GIVEN THE NEW NHC FORECAST...A HURRICANE WATCH HAS BEEN ISSUED FOR A 1242PORTION OF THE NORTHERN GULF COAST. 1243 1244FORECAST POSITIONS AND MAX WINDS 1245 1246INIT 26/0900Z 23.1N 79.0W 55 KT 65 MPH 1247 12H 26/1800Z 24.2N 80.8W 60 KT 70 MPH 1248 24H 27/0600Z 25.5N 83.1W 65 KT 75 MPH 1249 36H 27/1800Z 26.9N 84.9W 70 KT 80 MPH 1250 48H 28/0600Z 28.1N 86.5W 80 KT 90 MPH 1251 72H 29/0600Z 30.2N 88.0W 90 KT 105 MPH 1252 96H 30/0600Z 32.0N 88.5W 40 KT 45 MPH...INLAND 1253120H 31/0600Z 34.0N 88.5W 25 KT 30 MPH...INLAND 1254 1255$$ 1256FORECASTER BRENNAN 1257 1258 1259WTNT44 KNHC 261459 1260TCDAT4 1261 1262TROPICAL STORM ISAAC DISCUSSION NUMBER 22 1263NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 12641100 AM EDT SUN AUG 26 2012 1265 1266VISIBLE SATELLITE AND IMAGERY SUGGEST THAT THE TROPICAL CYCLONE IS 1267GRADUALLY BECOMING BETTER ORGANIZED. THERE ARE INDICATIONS OF 1268INNER CORE DEVELOPMENT WITH INCREASED CONVECTION NEAR AND OVER THE 1269CENTER...AND A PARTIAL EYEWALL IS IN EVIDENCE ON RADAR IMAGERY. THE 1270BANDING FEATURES HAVE BECOME MORE DISTINCT OVER THE NORTHERN AND 1271EASTERN SEMICIRCLES OF THE CIRCULATION. THE CURRENT INTENSITY 1272ESTIMATE IS HELD AT 55 KT PENDING OBSERVATIONS FROM AN AIR FORCE 1273HURRICANE HUNTER AIRCRAFT THAT SHOULD BE IN THE CENTER SHORTLY. 1274ISAAC CONTINUES TO EXHIBIT A WELL-DEFINED UPPER-LEVEL OUTFLOW 1275PATTERN...AND GRADUAL STRENGTHENING IS LIKELY AS THE CYCLONE 1276TRAVERSES THE EASTERN GULF OF MEXICO OVER THE NEXT COUPLE OF DAYS. 1277THE OFFICIAL WIND SPEED FORECAST IS SIMILAR TO THE PREVIOUS NHC 1278FORECAST AND IS ALSO CLOSE TO THE LATEST STATISTICAL-DYNAMICAL 1279GUIDANCE. 1280 1281THE TRACK FORECAST BEYOND DAY 2 HAS BECOME PROBLEMATIC. DYNAMICAL 1282MODELS DEPICT THE CYCLONE MOVING INTO A BREAK IN THE SUBTROPICAL 1283RIDGE NORTH OF THE GULF COAST IN ABOUT 72 HOURS. HOWEVER THERE IS 1284A LARGE SPREAD AMONG THE MORE RELIABLE TRACK MODELS. FOR EXAMPLE... 1285THE ECMWF FORECAST IS ABOUT 300 N MI EAST OF THE GFS SOLUTION AT DAY 12863. SINCE THE DYNAMICAL MODEL CONSENSUS HAS SHIFTED WESTWARD...THE 1287OFFICIAL TRACK FORECAST IS MOVED A BIT TO THE WEST OF THE PREVIOUS 1288ONE. THIS REQUIRES AN EXTENSION OF THE HURRICANE WATCH WESTWARD 1289ALONG THE LOUISIANA COAST. IT SHOULD BE NOTED THAT THERE IS 1290GREATER THAN USUAL UNCERTAINTY IN THE TRACK FORECAST. 1291 1292THROUGHOUT THE PERIOD...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT 1293FORECAST TRACK SINCE SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE 1294CENTER. 1295 1296 1297FORECAST POSITIONS AND MAX WINDS 1298 1299INIT 26/1500Z 23.9N 80.8W 55 KT 65 MPH 1300 12H 27/0000Z 25.0N 82.7W 65 KT 75 MPH 1301 24H 27/1200Z 26.1N 84.8W 70 KT 80 MPH 1302 36H 28/0000Z 27.4N 86.4W 75 KT 85 MPH 1303 48H 28/1200Z 28.5N 87.6W 80 KT 90 MPH 1304 72H 29/1200Z 30.5N 89.0W 90 KT 105 MPH 1305 96H 30/1200Z 32.5N 89.5W 30 KT 35 MPH...INLAND 1306120H 31/1200Z 34.5N 89.5W 20 KT 25 MPH...INLAND 1307 1308$$ 1309FORECASTER PASCH/ROBERTS 1310 1311 1312WTNT44 KNHC 262102 1313TCDAT4 1314 1315TROPICAL STORM ISAAC DISCUSSION NUMBER 23 1316NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1317500 PM EDT SUN AUG 26 2012 1318 1319ALTHOUGH SATELLITE AND RADAR IMAGES HAVE SUGGESTED THAT THE TROPICAL 1320CYCLONE WAS BECOMING A LITTLE BETTER ORGANIZED...AN AIR FORCE 1321HURRICANE HUNTER AIRCRAFT INVESTIGATING ISAAC THIS AFTERNOON HAVE 1322FOUND THAT THERE HAS BEEN NO STRENGTHENING OF THE STORM. 1323FLIGHT-LEVEL AND SFMR-OBSERVED WINDS SUPPORT AN INTENSITY OF 50 KT. 1324THERE IS STILL A WELL-ESTABLISHED UPPER-LEVEL OUTFLOW PATTERN OVER 1325THE SYSTEM...AND VERTICAL SHEAR SHOULD REMAIN FAIRLY LIGHT FOR THE 1326NEXT COUPLE OF DAYS. INTENSIFICATION STILL SEEMS LIKELY AS ISAAC 1327MOVES OVER THE EASTERN GULF...AND POSSIBLY OVER THE HIGHER HEAT 1328CONTENT OF THE LOOP CURRENT. THE OFFICIAL INTENSITY FOREAST IS 1329CLOSE TO THE LATEST LGEM GUIDANCE...AND NOT MUCH DIFFERENT FROM THE 1330PREVIOUS NHC FORECAST. 1331 1332ISAAC HAS MOVED A LITTLE TO THE LEFT OF PREVIOUS PROJECTIONS AND 1333CENTER FIXES YIELD A 6- TO 12-HOUR AVERAGED MOTION OF 295/15. THE 1334TRACK FORECAST CONTINUES TO BE CHALLENGING. THE DYNAMICAL MODELS 1335SHOW THE TROPICAL STORM/HURRICANE GRADUALLY TURNING TO THE RIGHT 1336AND HEADING FOR A BREAK IN THE SUBTROPICAL RIDGE. HOWEVER...THERE 1337ARE SUBSTANTIAL DIFFERENCES AMONG THE MOST RELIABLE MODELS AS TO 1338WHERE ISAAC MIGHT CROSS THE NORTHERN GULF COAST. THE U.K. MET. 1339OFFICE AND ECMWF MODELS ARE ABOUT 300 N MI TO THE EAST OF THE GFS 1340AT LANDFALL. IT SHOULD BE NOTED THAT NEARLY ALL OF THE GFS ENSMEBLE 1341MEMBERS ARE EAST OF THE GFS CONTROL TRACK. BECAUSE OF THE WIDE 1342MODEL SPREAD...THERE CONTINUES TO BE GREATER THAN USUAL TRACK 1343FORECAST UNCERTAINTY. 1344 1345THROUGHOUT THE PERIOD...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT 1346FORECAST TRACK DUE TO FORECAST UNCERTAINTIES AND THE FACT THAT 1347SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER. 1348 1349THE OFFICIAL FORECAST TRACK AND WIND RADII NECESSITATE THE ISSUANCE 1350OF A HURRICANE WARNING FOR THE NORTHERN GULF COAST AT THIS TIME. 1351 1352FORECAST POSITIONS AND MAX WINDS 1353 1354INIT 26/2100Z 24.2N 82.3W 50 KT 60 MPH 1355 12H 27/0600Z 25.1N 83.9W 55 KT 65 MPH 1356 24H 27/1800Z 26.3N 85.9W 60 KT 70 MPH 1357 36H 28/0600Z 27.7N 87.6W 70 KT 80 MPH 1358 48H 28/1800Z 28.9N 88.5W 80 KT 90 MPH 1359 72H 29/1800Z 30.7N 89.5W 85 KT 100 MPH...INLAND 1360 96H 30/1800Z 32.5N 90.0W 30 KT 35 MPH...INLAND 1361120H 31/1800Z 34.5N 90.0W 20 KT 25 MPH...INLAND 1362 1363$$ 1364FORECASTER PASCH 1365 1366 1367WTNT44 KNHC 270250 1368TCDAT4 1369 1370TROPICAL STORM ISAAC DISCUSSION NUMBER 24 1371NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 13721100 PM EDT SUN AUG 26 2012 1373 1374SATELLITE IMAGERY HAS SHOWN AN INCREASE IN THE AREA OF COLD CLOUD 1375TOPS NEAR THE CENTER OF ISAAC. HOWEVER...THERE HAS NOT BEEN ANY 1376SIGNIFICANT CHANGE IN ORGANIZATION IN RADAR DATA FROM KEY WEST 1377THIS EVENING. IN FACT...THE AIRCRAFT FIXES HAVE BEEN NEAR THE 1378SOUTHEASTERN EDGE OF THE CONVECTIVE CLUSTER SEEN IN BOTH SATELLITE 1379AND RADAR IMAGERY. AN EARLIER SHIP OBSERVATION AND SFMR 1380MEASUREMENTS OF 50-55 KT SUPPORTED INCREASING THE INTENSITY TO 55 1381KT ON THE INTERMEDIATE ADVISORY. SINCE THAT TIME...THE AIRCRAFT 1382HAS NOT FOUND ANY STRONGER WINDS SO THE INITIAL WIND SPEED REMAINS 1383UNCHANGED. THE LARGE SCALE ENVIRONMENTAL FACTORS...WARM 1384WATERS...AND A CONDUCIVE UPPER-AIR PATTERN FAVOR STRENGTHENING 1385DURING THE NEXT COUPLE OF DAYS. HOWEVER...THE LACK OF AN INNER CORE 1386AND LARGE WIND FIELD COULD CONTINUE TO BE IMPEDING FACTORS FOR 1387SIGNIFICANT STRENGTHENING IN THE SHORT TERM. THE NHC INTENSITY 1388FORECAST SHOWS A GRADUAL INCREASE IN WIND SPEED DURING THE NEXT 12 1389HOURS OR SO...FOLLOWED BY MORE STEADY STRENGTHENING. THE OFFICIAL 1390FORECAST IS CLOSE TO THE SHIPS/LGEM GUIDANCE AND THE INTENSITY 1391CONSENSUS. 1392 1393AIRCRAFT AND RADAR CENTER FIXES INDICATE THAT ISAAC JOGGED WESTWARD 1394AND SLOWED DOWN THIS EVENING. HOWEVER...THE LONGER TERM MOTION IS 1395285/12 KT. THE MODELS SHOW ISAAC TURNING TOWARD THE NORTHWEST INTO 1396A BREAK IN THE SUBTROPICAL RIDGE. ALTHOUGH THE MODELS AGREE ON 1397THIS TURN...THERE IS AN UNUSUALLY LARGE SPREAD IN THE TRACK GUIDANCE 1398AFTER 24 HOURS. THE SPREAD OF LANDFALL LOCATIONS ALONG THE NORTHERN 1399GULF COAST RANGES FROM THE TEXAS/LOUISIANA BORDER EASTWARD TO THE 1400ALABAMA/FLORIDA BORDER WITH THE HWRF...GFDL...AND GFS NEAR THE 1401WESTERN EDGE AND THE UKMET AND ECMWF ALONG THE EASTERN EDGE OF THE 1402ENVELOPE. OVERALL...THE CONSENSUS HAS SHIFTED A LITTLE WESTWARD 1403AND THE OFFICIAL FORECAST AS BEEN MOVED IN THAT DIRECTION. THE NHC 1404FORECAST IS BETWEEN THE ECMWF AND GFS ENSEMBLE MEANS AND NEAR THE 1405HFIP MULTI-MODEL CONSENSUS. BECAUSE OF THE VERY LARGE SPREAD IN 1406THE GUIDANCE...THERE CONTINUES TO BE GREATER THAN USUAL TRACK 1407FORECAST UNCERTAINTY. 1408 1409THROUGHOUT THE PERIOD...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT 1410FORECAST TRACK DUE TO FORECAST UNCERTAINTIES AND THE FACT THAT 1411SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER. 1412 1413FORECAST POSITIONS AND MAX WINDS 1414 1415INIT 27/0300Z 24.2N 82.9W 55 KT 65 MPH 1416 12H 27/1200Z 25.2N 84.8W 60 KT 70 MPH 1417 24H 28/0000Z 26.5N 86.7W 70 KT 80 MPH 1418 36H 28/1200Z 27.9N 88.3W 80 KT 90 MPH 1419 48H 29/0000Z 28.9N 89.3W 85 KT 100 MPH 1420 72H 30/0000Z 30.6N 90.3W 70 KT 80 MPH...INLAND 1421 96H 31/0000Z 33.0N 91.0W 30 KT 35 MPH...INLAND 1422120H 01/0000Z 36.0N 91.0W 20 KT 25 MPH...INLAND 1423 1424$$ 1425FORECASTER BROWN 1426 1427 1428WTNT44 KNHC 270859 1429TCDAT4 1430 1431TROPICAL STORM ISAAC DISCUSSION NUMBER 25 1432NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1433500 AM EDT MON AUG 27 2012 1434 1435THE LAST AIRCRAFT FIX BEFORE 06Z SUGGESTED THAT THE CENTER OF ISAAC 1436HAD REFORMED A LITTLE CLOSER TO THE DEEP CONVECTION...AND THAT THE 1437PRESSURE HAD FALLEN TO 990 MB. HOWEVER...NO STRONGER WINDS WERE 1438OBSERVED BY THE AIRCRAFT...AND THE INITIAL INTENSITY IS HELD AT 55 1439KT FOR THIS ADVISORY. THE CONTINUED LACK OF INNER CORE STRUCTURE... 1440THE LARGE CIRCULATION...AND SOUTHEASTERLY SHEAR NEAR THE OUTFLOW 1441LAYER DUE TO AN UPPER-LEVEL LOW SOUTHWEST OF ISSAC SHOULD RESULT IN 1442ONLY GRADUAL STRENGTHENING FOR THE FIRST 12 HOURS OR SO. AFTER THAT 1443TIME...STEADIER STRENGTHENING IS EXPECTED AS THE CIRCULATION 1444CONSOLIDATES AND AS THE UPPER LOW MOVES AWAY FROM ISAAC. THE NEW 1445NHC FORECAST IS A LITTLE LOWER THAN THE PREVIOUS ONE...AND IS CLOSE 1446TO OR A BIT ABOVE THE INTENSITY CONSENSUS UNTIL LANDFALL IN ABOUT 144748 HOURS. 1448 1449RECENT AIRCRAFT FIXES SHOW THE CENTER IS NOW LOCATED CLOSER TO THE 1450DEEP CONVECTION. THE INITIAL MOTION ESTIMATE IS 300/12...AS ISAAC 1451IS SITUATED ON THE SOUTHWESTERN PERIPHERY OF THE ATLANTIC 1452SUBTROPICAL RIDGE. A DECREASE IN FORWARD SPEED AND A TURN TOWARD 1453THE NORTHWEST ARE EXPECTED IN THE NEXT DAY OR SO...AS ISAAC MOVES 1454INTO A BREAK IN THE RIDGE OVER THE NORTHERN GULF OF MEXICO INDUCED 1455BY A TROUGH MOVING THROUGH THE EASTERN UNITED STATES. THE TRACK 1456MODEL GUIDANCE IS PRETTY TIGHTLY CLUSTERED FOR THE FIRST 36 HOURS 1457OR SO...AND THROUGH THAT TIME THE NEW NHC FORECAST IS A LITTLE TO 1458THE RIGHT OF THE PREVIOUS ONE DUE TO THE INITIAL POSITION AND 1459MOTION. WHILE THE MODEL SPREAD INCREASES AT 48 HOURS AND BEYOND... 1460THE ECMWF AND UKMET HAVE SHIFTED WESTWARD THIS CYCLE AND NOW TAKE 1461ISAAC TOWARD THE MISSISSIPPI COAST. THE GFS...GFS ENSEMBLE MEAN... 1462GFDL...AND HWRF CONTINUE TO SHOW LESS OF A NORTHWARD TURN AND BRING 1463THE CYCLONE INTO SOUTHEASTERN LOUISIANA. THE NEW NHC TRACK FORECAST 1464HAS BEEN ADJUSTED WESTWARD BY ABOUT A DEGREE AT 72 HOURS AND BEYOND 1465AND LIES BETWEEN THE ECMWF AND THE GFS ENSEMBLE MEAN. BECAUSE OF 1466THE LARGE SPREAD IN THE GUIDANCE...THE UNCERTAINTY IN THE TRACK 1467FORECAST CONTINUES TO BE GREATER THAN USUAL AT 48 HOURS AND BEYOND. 1468 1469BECAUSE OF THIS UNCERTAINTY...AND THE FACT THAT SIGNIFICANT HAZARDS 1470EXTEND WELL AWAY FROM THE CENTER...IT IS IMPORTANT NOT TO FOCUS ON 1471THE EXACT FORECAST TRACK. 1472 1473GIVEN THE NEW TRACK AND INTENSITY FORECAST...NEW WATCHES AND 1474WARNINGS HAVE BEEN ISSUED FOR PORTIONS OF THE LOUISIANA COAST. THE 1475INITIAL 34-KT WIND RADII HAVE BEEN EXPANDED IN THE SOUTHEAST 1476SEMICIRCLE GIVEN CONTINUING OBSERVATIONS OF TROPICAL STORM 1477CONDITIONS IN THE FLORIDA KEYS. 1478 1479FORECAST POSITIONS AND MAX WINDS 1480 1481INIT 27/0900Z 25.2N 84.2W 55 KT 65 MPH 1482 12H 27/1800Z 26.2N 85.9W 60 KT 70 MPH 1483 24H 28/0600Z 27.6N 87.8W 70 KT 80 MPH 1484 36H 28/1800Z 28.8N 89.1W 75 KT 85 MPH 1485 48H 29/0600Z 29.7N 90.1W 80 KT 90 MPH...INLAND 1486 72H 30/0600Z 31.2N 91.1W 50 KT 60 MPH...INLAND 1487 96H 31/0600Z 34.0N 92.0W 30 KT 35 MPH...INLAND 1488120H 01/0600Z 38.0N 91.5W 20 KT 25 MPH...INLAND 1489 1490$$ 1491FORECASTER BRENNAN 1492 1493 1494WTNT44 KNHC 271458 1495TCDAT4 1496 1497TROPICAL STORM ISAAC DISCUSSION NUMBER 26 1498NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 14991000 AM CDT MON AUG 27 2012 1500 1501DATA FROM THE TAMPA AND KEY WEST DOPPLER RADARS...AND FROM AIR FORCE 1502RESERVE AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE THE INNER 1503CORE STRUCTURE AND INTENSITY OF ISAAC HAS CHANGED LITTLE SINCE THE 1504PREVIOUS ADVISORY. A RAGGED EYE FEATURE HAS OCCASIONALLY APPEARED 1505IN THESE DATA...BUT IT HAS BEEN UNABLE TO PERSIST. THE CENTRAL 1506PRESSURE HAS DECREASED TO AROUND 987-988 MB...BUT THIS HAS NOT 1507RESULTED IN ANY INCREASE IN THE WIND SPEEDS. THE PREVIOUS INTENSITY 1508OF 55 KT IS BEING MAINTAINED FOR THIS ADVISORY BASED ON THE RECON 1509WIND DATA. 1510 1511THE INITIAL MOTION ESTIMATE IS 305/12. NO SIGNIFICANT CHANGE WAS 1512MADE TO THE PREVIOUS FORECAST TRACK. THE LATEST 12Z UPPER-AIR DATA 1513INDICATE 20-40 METER HEIGHT RISES AT THE 500 MB AND 400 MB LEVELS 1514ACROSS THE SOUTHEASTERN AND SOUTH-CENTRAL U.S....WHICH SUGGESTS 1515THAT THE SUBTROPICAL RIDGE TO THE NORTH OF ISAAC HAS STRENGTHENED 1516SLIGHTLY. THIS WOULD SUPPORT A NORTHWESTWARD TO WEST-NORTHWESTWARD 1517MOTION UNTIL LANDFALL IN ABOUT 36-48 HOURS...AND THIS MOTION IS 1518SUPPORTED BY THE NHC MODEL CONSENSUS. AFTER 48 HOURS...HOWEVER... 1519THE MODEL GUIDANCE IS WIDELY DIVERGENT WITH A SPREAD OF MORE THAN 1520500 N MI BETWEEN THE GFS ON THE LEFT AND THE ECMWF ON THE RIGHT. 1521THE FORECAST TRACK AT DAYS 3-5 IS ALSO SIMILAR TO THE PREVIOUS 1522ADVISORY AND LIES CLOSE TO THE MODEL CONSENSUS...BUT THIS IS A LOW 1523CONFIDENCE FORECAST AT THOSE TIME PERIODS. 1524 1525THE LACK OF STRENGTHENING APPEARS TO TO BE DUE TO THE 1526LARGER-THAN-AVERAGE WIND RADII...WHICH HAVE YET TO CONTRACT 1527INWARD...ALONG WITH THE PERIODIC ENTRAINMENT OF DRY MID-LEVEL AIR 1528FROM THE EASTERN SEMICIRCLE INTO THE INNER-CORE REGION. UNTIL THE 1529DRY AIR MIXES OUT...EROSION OF THE INNER-CORE CONVECTION WILL 1530LIKELY CONTINUE UNTIL ISAAC APPROACHES THE NORTH-CENTRAL GULF COAST 1531IN ABOUT 24 HOURS. AT THAT TIME...INCREASED FRICTIONAL EFFECTS FROM 1532THE GULF COAST LAND MASS IS EXPECTED TO CONTRIBUTE TO AN INCREASE 1533IN CONVECTION IN THE NORTHEAST QUADRANT...WHICH COULD ENABLE THE 1534STRENGTHENING PROCESS. THE OFFICIAL INTENSITY FORECAST IS SIMILAR 1535TO THE PREVIOUS ADVISORY AND IS SLIGHTLY ABOVE THE INTENSITY 1536CONSENSUS MODEL IV15. 1537 1538BECAUSE SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER...IT IS 1539IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK. 1540 1541FORECAST POSITIONS AND MAX WINDS 1542 1543INIT 27/1500Z 26.1N 85.3W 55 KT 65 MPH 1544 12H 28/0000Z 27.1N 86.8W 65 KT 75 MPH 1545 24H 28/1200Z 28.3N 88.4W 70 KT 80 MPH 1546 36H 29/0000Z 29.3N 89.6W 80 KT 90 MPH 1547 48H 29/1200Z 30.2N 90.5W 70 KT 80 MPH...INLAND 1548 72H 30/1200Z 31.9N 91.7W 40 KT 45 MPH...INLAND 1549 96H 31/1200Z 35.2N 92.3W 25 KT 30 MPH...INLAND 1550120H 01/1200Z 39.3N 91.3W 20 KT 25 MPH...INLAND 1551 1552$$ 1553FORECASTER STEWART 1554 1555 1556WTNT44 KNHC 272058 1557TCDAT4 1558 1559TROPICAL STORM ISAAC DISCUSSION NUMBER 27 1560NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1561400 PM CDT MON AUG 27 2012 1562 1563THE MUCH ANTICIPATED INTENSIFICATION PROCESS APPEARS TO HAVE FINALLY 1564STARTED BASED ON REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE 1565AIRCRAFT AND FROM NEARBY NOAA BUOY 42003. THE CENTRAL PRESSURE HAS 1566DECREASED BY AT LEAST 7 MB SINCE THE PREVIOUS ADVISORY. THE HIGHEST 1567FLIGHT-LEVEL WINDS OBSERVED HAVE BEEN 74 KT IN THE SOUTHWEST 1568QUADRANT AND THE HIGHEST BIAS-ADJUSTED SFMR WINDS ARE NEAR 58 KT. 1569THESE DATA SUPPORT AN INTENSITY OF 60 KT. 1570 1571ISAAC WOBBLED WESTWARD THIS AFTERNOON...BUT A REPRESENTATIVE INITIAL 1572MOTION ESTIMATE IS 305/10. THE LATEST 12Z NHC MODEL GUIDANCE IS IN 1573BETTER AGREEMENT ON A WEST-NORTHWEST TO NORTHWEST MOTION TOWARD THE 1574SOUTHEAST LOUISIANA AND MISSISSIPPI COASTAL AREAS OVER THE NEXT 157536-48 HOURS. AFTER 48 HOURS...HOWEVER...THE MODEL GUIDANCE REMAINS 1576DIVERGENT ON THE HANDLING OF A SHORTWAVE TROUGH FORECAST TO DIG 1577SOUTHEASTWARD FROM THE UPPER MIDWEST AND INTO THE MID-ATLANTIC 1578REGION...FOLLOWED BY A RIDGE BUILDING IN BEHIND THE TROUGH. THE GFS 1579AND ECMWF...OUR MOST RELIABLE MODELS... NOW HAVE VERY SIMILAR 1580SOLUTIONS THROUGH DAY 5...AND THE OFFICIAL FORECAST TRACK IS 1581BETWEEN THOSE TWO MODELS. 1582 1583SATELLITE DATA INDICATE ISAAC HAS BECOME BETTER ORGANIZED OVER THE 1584PAST 6 HOURS WITH THE DEVELOPMENT OF A CENTRAL DENSE OVERCAST CLOUD 1585PATTERN OVER THE CENTER ALONG WITH A DEVELOPING EYE IN RECON DATA. 1586SATELLITE DATA T-NUMBERS HAVE INCREASED TO T4.5/77 KT FROM TAFB AND 1587SAB. RECON WIND DATA INDICATE THE RADIUS OF MAXIMUM WINDS HAS ALSO 1588PULLED INWARD TO ABOUT 30 N MI. ALTHOUGH ADDITIONAL CONVECTION HAS 1589BEEN DEVELOPING IN THE NORTHEASTERN QUADRANT...DRY MID-LEVEL AIR 1590STILL LURKS JUST TO THE EAST AND SOUTHEAST OF THE CDO FEATURE... 1591WHICH COULD BE ENTRAINED INTO THE INNER CORE AT ANY TIME AND 1592DISRUPT THE DEVELOPMENT PROCESS. DUE TO THE PROXIMITY OF DRY 1593AIR...THE INTENSITY FORECAST INDICATES ONLY MODEST DEVELOPMENT FOR 1594THE NEXT 24 HOURS. HOWEVER...STRENGTHENING IS EXPECTED TO CONTINUE 1595RIGHT UP UNTIL LANDFALL OCCURS DUE TO THE VERY WARM WATERS THE 1596CYCLONE WILL BE PASSING OVER AND THE VERY FAVORABLE UPPER-LEVEL 1597OUTFLOW REGIME THAT ISAAC IS FORECAST TO DEVELOP BY 24 HOURS. THE 1598INTENSITY FORECAST IS JUST SLIGHTLY HIGHER THAN THE MODEL GUIDANCE. 1599 1600BECAUSE SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER...IT IS 1601IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK. THE SLOW FORWARD 1602SPED OF AROUND 5 KT AFTER LANDFALL WILL RESULT IN A HEAVY RAIN AND 1603FLOOD SITUATION FOR PORTIONS OF THE CENTRAL GULF COAST AND LOWER 1604MISSISSIPPI VALLEY REGIONS. 1605 1606FORECAST POSITIONS AND MAX WINDS 1607 1608INIT 27/2100Z 26.4N 86.2W 60 KT 70 MPH 1609 12H 28/0600Z 27.4N 87.5W 70 KT 80 MPH 1610 24H 28/1800Z 28.6N 89.0W 80 KT 90 MPH 1611 36H 29/0600Z 29.5N 90.0W 85 KT 100 MPH...NEAR THE COAST 1612 48H 29/1800Z 30.3N 90.7W 75 KT 85 MPH...INLAND 1613 72H 30/1800Z 32.2N 91.8W 35 KT 40 MPH...INLAND 1614 96H 31/1800Z 35.9N 92.1W 25 KT 30 MPH...INLAND 1615120H 01/1800Z 38.7N 89.3W 20 KT 25 MPH...INLAND 1616 1617$$ 1618FORECASTER STEWART 1619 1620 1621WTNT44 KNHC 280255 1622TCDAT4 1623 1624TROPICAL STORM ISAAC DISCUSSION NUMBER 28 1625NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 16261000 PM CDT MON AUG 27 2012 1627 1628THE SATELLITE PRESENTATION OF ISAAC HAS NOT CHANGED VERY MUCH DURING 1629THE PAST FEW HOURS. INFRARED AND MICROWAVE IMAGERY SHOW A STRONG 1630BAND OF CONVECTION...PERHAPS THE BEGINNING OF AN EYEWALL...WRAPPING 1631AROUND THE SOUTH AND EAST PORTIONS OF THE CIRCULATION. HOWEVER... 1632AIRCRAFT OBSERVATIONS INDICATE THAT THE CONVECTIVE BAND WAS OPEN TO 1633THE NORTHWEST AND THAT THE LOW-LEVEL CENTER WAS DISPLACED A LITTLE 1634TO THE SOUTH OF THE ROTATION SEEN IN SATELLITE PICTURES. THE 1635MINIMUM PRESSURE HAS NOT FALLEN SIGNIFICANTLY DURING THE PAST 1636SEVERAL HOURS AND THE NOAA AND AIR FORCE AIRCRAFT HAVE NOT REPORTED 1637WINDS ANY HIGHER THAN WHAT WAS MEASURED LATE THIS AFTERNOON. 1638THEREFORE...ISAAC REMAINS A 60-KT TROPICAL STORM FOR THIS ADVISORY. 1639ISAAC CONTINUES TO HAVE DIFFICULTLY MAINTAINING DEEP CONVECTION 1640OVER THE NORTHERN SEMICIRCLE LIKELY DUE TO SOME DRY AIR 1641ENTRAINMENT. OTHERWISE...ENVIRONMENTAL CONDITIONS SHOULD BE 1642CONDUCIVE FOR STRENGTHENING UNTIL LANDFALL. ISAAC IS FORECAST TO 1643BECOME A HURRICANE OVERNIGHT AND NHC INTENSITY FORECAST IS SLIGHTLY 1644HIGHER THAN MOST OF THE GUIDANCE. 1645 1646ISAAC HAS BEEN MOVING NORTHWESTWARD OR 310 DEGREES AT 9 KT. THE 1647TRACK GUIDANCE HAS CONTINUED TO COME INTO BETTER AGREEMENT DURING 1648THE FIRST 36 TO 48 HOURS OF THE FORECAST PERIOD. ISAAC SHOULD MOVE 1649NORTHWESTWARD TOWARD THE NORTH-CENTRAL GULF COAST WHERE A BREAK IN 1650THE SUBTROPICAL RIDGE IS LOCATED. AS A MID-LATITUDE TROUGH 1651BYPASSES ISAAC IN A DAY OR SO...SOME RIDGING BUILDS TO THE 1652NORTHWEST OF THE CYCLONE. THIS IS EXPECTED TO CAUSE ISAAC TO 1653SLOW DOWN AS IT MOVES INLAND. AFTER 72 HOURS...THE CYCLONE SHOULD 1654BEGIN TO MOVE A LITTLE FASTER TOWARD THE NORTH AND NORTHEAST AS IT 1655MOVES AROUND THE WESTERN SIDE OF A MID-LEVEL RIDGE THAT SLIDES 1656EASTWARD ACROSS THE OHIO VALLEY AND MID-ATLANTIC REGIONS. THE NEW 1657NHC TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND REMAINS BETWEEN 1658THE ECMWF AND GFS MODELS. 1659 1660ISAAC IS A LARGE TROPICAL CYCLONE. A DANGEROUS STORM SURGE...HEAVY 1661RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE CENTER AND 1662ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN GULF COAST. 1663THE THREAT OF HEAVY RAINFALL AND FLOODING IS ALSO EXPECTED TO 1664SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY REGION DURING THE 1665NEXT FEW DAYS. 1666 1667 1668FORECAST POSITIONS AND MAX WINDS 1669 1670INIT 28/0300Z 27.1N 87.0W 60 KT 70 MPH 1671 12H 28/1200Z 28.0N 88.0W 70 KT 80 MPH 1672 24H 29/0000Z 29.1N 89.2W 80 KT 90 MPH...ON THE COAST 1673 36H 29/1200Z 29.9N 90.1W 65 KT 75 MPH...INLAND 1674 48H 30/0000Z 30.7N 90.7W 50 KT 60 MPH...INLAND 1675 72H 31/0000Z 33.3N 91.7W 30 KT 35 MPH...INLAND 1676 96H 01/0000Z 37.5N 91.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 1677120H 02/0000Z 40.5N 87.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 1678 1679$$ 1680FORECASTER BROWN/BLAKE 1681 1682 1683WTNT44 KNHC 280856 1684TCDAT4 1685 1686TROPICAL STORM ISAAC DISCUSSION NUMBER 29 1687NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1688400 AM CDT TUE AUG 28 2012 1689 1690REPORTS FROM THE AIR FORCE HURRICANE HUNTER AIRCRAFT INDICATE THAT 1691THE CENTRAL PRESSURE HAS DROPPED A LITTLE MORE...BUT SO FAR...THE 1692MAXIMUM FLIGHT-LEVEL AND SFMR-OBSERVED SURFACE WINDS STILL DO NOT 1693QUITE SUPPORT HURRICANE INTENSITY. THE CURRENT INTENSITY IS HELD 1694AT 60 KT PENDING ADDITIONAL OBSERVATIONS FROM THE HURRICANE 1695HUNTERS. ALTHOUGH THE WIND FIELD REMAINS RATHER BROAD AND 1696RELATIVELY FLAT...RECENT AIRCRAFT DATA SUGGEST THAT THE MAXIMUM 1697WINDS ARE NOW OCCURRING SOMEWHAT CLOSER TO THE CENTER OVER THE 1698NORTHERN SEMICIRCLE OF THE CYCLONE. THIS WOULD SUGGEST THAT THE 1699INNER CORE CIRCULATION IS BECOMING BETTER DEFINED...AND 1700STRENGTHENING MIGHT BE IMMINENT. UPPER-LEVEL OUTFLOW IS 1701WELL-ESTABLISHED OVER THE SOUTHERN SEMICIRCLE OF THE SYSTEM...BUT 1702CENTRAL CONVECTION CONTINUES TO FLUCTUATE. THE LATTER IS 1703PRESUMABLY DUE TO A CONTINUED INTRUSION OF DRY AIR INTO THE CORE 1704REGION. THE STATISTICAL-DYNAMICAL GUIDANCE IS A LITTLE LOWER THAN 1705IN PREVIOUS RUNS...AND THE STORM HAS ONLY ABOUT 12-24 HOURS BEFORE 1706MOVING INLAND. THE OFFICIAL INTENSITY FORECAST IS JUST SLIGHTLY 1707LOWER THAN THE PREVIOUS ONE. 1708 1709CENTER FIXES FROM THE AIRCRAFT INDICATE THAT THE STORM HAS WOBBLED 1710ON A GENERALLY WESTWARD COURSE OVER THE PAST FEW HOURS. THIS IS 1711BELIEVED TO BE TEMPORARY...HOWEVER...AND THE LONGER-TERM MOTION 1712ESTIMATE IS ABOUT 305/10. THE CURRENT AND FORECAST STEERING REGIME 1713ARE BASICALLY THE SAME AS IN THE PREVIOUS PACKAGE. ISAAC IS 1714EXPECTED TO MOVE INTO A WEAKNESS IN THE SUBTROPICAL RIDGE NEAR THE 1715NORTH-CENTRAL GULF COAST...WITH SOME SLOWING OF FORWARD SPEED 1716DURING THE NEXT COUPLE OF DAYS AS A RIDGE BUILDS A LITTLE TO THE 1717NORTHWEST OF THE CYCLONE. LATER ON...THE SYSTEM SHOULD TURN 1718NORTHWARD AND NORTHEASTWARD INTO THE OHIO VALLEY REGION AS IT MOVES 1719AROUND THE WESTERN PERIPHERY OF A MID-LEVEL ANTICYCLONE. 1720 1721ISAAC IS A LARGE TROPICAL CYCLONE. A DANGEROUS STORM SURGE...HEAVY 1722RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE CENTER AND 1723ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN GULF COAST. 1724FOR THIS REASON...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT CENTER 1725LOCATION. THE THREAT OF HEAVY RAINFALL AND FLOODING IS ALSO 1726EXPECTED TO SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY REGION 1727DURING THE NEXT FEW DAYS. 1728 1729FORECAST POSITIONS AND MAX WINDS 1730 1731INIT 28/0900Z 27.5N 88.1W 60 KT 70 MPH 1732 12H 28/1800Z 28.5N 89.1W 70 KT 80 MPH 1733 24H 29/0600Z 29.5N 90.1W 75 KT 85 MPH...NEAR THE COAST 1734 36H 29/1800Z 30.3N 90.9W 55 KT 65 MPH...INLAND 1735 48H 30/0600Z 31.4N 91.5W 45 KT 50 MPH...INLAND 1736 72H 31/0600Z 34.5N 92.5W 25 KT 30 MPH...INLAND 1737 96H 01/0600Z 38.0N 91.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 1738120H 02/0600Z 40.5N 87.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 1739 1740$$ 1741FORECASTER PASCH 1742 1743 1744WTNT44 KNHC 281459 1745TCDAT4 1746 1747TROPICAL STORM ISAAC DISCUSSION NUMBER 30 1748NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 17491000 AM CDT TUE AUG 28 2012 1750 1751REPORTS FROM AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT INDICATE 1752THE CENTRAL PRESSURE HAS DECREASED TO ABOUT 976 MB SINCE THE 1753PREVIOUS ADVISORY...BUT IT HAS LEVELED OFF OVER THE PAST FEW HOURS. 1754THE MAXIMUM 850 MB FLIGHT-LEVEL WIND OBSERVED HAS BEEN 89 KT... 1755WHICH EQUATES TO A SURFACE WIND OF ABOUT 71 KT. HOWEVER... 1756BIAS-ADJUSTED SFMR SURFACE WINDS HAVE ONLY BEEN AROUND 60-62 KT... 1757WHICH CORRELATES WELL WITH DROPSONDE BOUNDARY LAYER-DERIVED SURFACE 1758WINDS. AS SUCH...THE INTENSITY OF ISAAC IS BEING MAINTAINED AT 60 1759KT...WHICH IS JUST BELOW HURRICANE STATUS. 1760 1761CENTER FIXES FROM THE AIRCRAFT INDICATE THAT ISAAC HAS BEEN WOBBLING 1762IN A GENERAL NORTHWESTWARD MOTION OF 310/09 KT. THERE REMAINS NO 1763SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. 1764ISAAC IS FORECAST TO MOVE INTO A WEAKNESS IN THE SUBTROPICAL RIDGE 1765NEAR THE NORTH-CENTRAL GULF COAST OVER THE NEXT 24-36 HOURS... 1766ACCOMPANIED BY A GRADUAL DECREASE IN THE FORWARD SPEED. AS THE 1767RIDGE BUILDS BACK IN TO THE NORTH OF THE CYCLONE...ISAAC IS 1768EXPECTED TO TURN A LITTLE MORE TOWARD THE WEST-NORTHWEST BEFORE IT 1769TURNS NORTHWARD ON DAY 4...AND MOVES NORTHEASTWARD INTO THE OHIO 1770VALLEY REGION ON DAY 5. THE OFFICIAL FORECAST TRACK HAS BEEN NUDGED 1771A LITTLE TO THE LEFT OF THE PREVIOUS ADVISORY TRACK AND LIES JUST 1772TO THE RIGHT OF THE CONSENSUS MODELS TV15 AND TCVA. 1773 1774MID-LEVEL DRY AIR ENTRAINMENT CONTINUES TO PLAGUE ISAAC. AS SOON AS 1775THE CYCLONE DEVELOPS INNER-CORE CONVECTION AND THE APPEARANCE OF AN 1776EYE IN RADAR AND SATELLITE IMAGERY...THE CONVECTION ERODES DUE TO 1777THE DRY AIR. DESPITE THE FAVORABLE OCEANIC CONDITIONS AND 1778UPPER-LEVEL OUTFLOW REGIME...ISAAC ONLY HAS ABOUT 12-18 HOURS FOR 1779FURTHER STRENGTHENING TO OCCUR. THE OFFICIAL INTENSITY FORECAST IS 1780SIMILAR TO THE PREVIOUS ADVISORY...WITH ONLY TIMING ADJUSTMENTS 1781MADE TO THE INTENSITY FORECAST...AND CLOSELY FOLLOWS THE INTENSITY 1782MODEL CONSENSUS. 1783 1784ISAAC IS A LARGE TROPICAL CYCLONE. A DANGEROUS STORM SURGE...HEAVY 1785RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE CENTER AND 1786ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN GULF COAST. 1787FOR THIS REASON...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT CENTER 1788LOCATION. THE THREAT OF HEAVY RAINFALL AND FLOODING IS ALSO 1789EXPECTED TO SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY REGION 1790DURING THE NEXT FEW DAYS. 1791 1792FORECAST POSITIONS AND MAX WINDS 1793 1794INIT 28/1500Z 28.1N 88.5W 60 KT 70 MPH 1795 12H 29/0000Z 28.8N 89.4W 70 KT 80 MPH 1796 24H 29/1200Z 29.7N 90.4W 65 KT 75 MPH...INLAND 1797 36H 30/0000Z 30.5N 91.5W 45 KT 50 MPH...INLAND 1798 48H 30/1200Z 32.0N 92.0W 35 KT 40 MPH...INLAND 1799 72H 31/1200Z 35.0N 92.5W 20 KT 25 MPH...INLAND 1800 96H 01/1200Z 38.5N 90.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 1801120H 02/1200Z 41.0N 86.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 1802 1803$$ 1804FORECASTER STEWART 1805 1806 1807WTNT44 KNHC 282053 1808TCDAT4 1809 1810HURRICANE ISAAC DISCUSSION NUMBER 31 1811NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1812400 PM CDT TUE AUG 28 2012 1813 1814SINCE THE LAST RECON FLIGHTS INTO ISAAC...WHEN A BIAS-CORRECTED SFMR 1815WIND OF 64 KT WAS OBSERVED...THE RADAR AND SATELLITE APPEARANCE HAS 1816CONTINUED TO BECOME BETTER DEFINED. ON THIS BASIS...THE ESTIMATED 1817INTENSITY HAS BEEN INCREASED TO 70 KT. 1818 1819TRENDING THROUGH ALL OF THE WIGGLES AND WOBBLES IN THE AIRCRAFT 1820FIXES YIELDS A GENERAL NORTHWESTWARD MOTION OF 310/07 KT. ISAAC 1821REMAINS ON TRACK...AND THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE 1822EARLY PART OF THE FORECAST. ISSAC IS EXPECTED TO CONTINUE 1823NORTHWESTWARD TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE THAT IS 1824ORIENTED EAST-WEST ALONG 30N LATITUDE. BECAUSE OF THIS WEAKNESS... 1825THE STEERING FLOW IS FORECAST TO DECREASE OVER THE NEXT 36-48 1826HOURS...WHICH WILL RESULT IN ISAAC SLOWING DOWN SOME MORE. 1827AFTERWARDS...THE RIDGE IS FORECAST TO BUILD BACK IN BY ALL OF THE 1828MODELS...ALBEIT TO VARYING DEGREES...WHICH SHOULD CAUSE THE CYCLONE 1829TO TURN SLIGHTLY TOWARD THE WEST-NORTHWEST BEFORE IT TURNS 1830NORTHWARD BY DAY 4...AND THEN MOVE NORTHEASTWARD INTO THE LOWER 1831GREAT LAKES AND OHIO VALLEY REGIONS BY DAY 5. IN THE LATTER PART OF 1832THE FORECAST PERIOD THE FORECAST HAS BEEN NUDGED A LITTLE TO THE 1833LEFT OF THE PREVIOUS TRACK...BUT REMAINS TO THE RIGHT OF THE 1834CONSENSUS MODELS THAT HAVE RECENTLY HAD A LEFTWARD BIAS. 1835 1836ALTHOUGH NOT EXPLICITLY FORECAST DUE TO LAND INTERACTION AT 12 1837HOURS...FAVORABLE WATER TEMPERATURES ALONG WITH AN IMPRESSIVE 1838UPPER-LEVEL OUTFLOW REGIME SUGGEST THAT ISAAC COULD STRENGTHEN A 1839LITTLE MORE BEFORE LANDFALL OCCURS. HOWEVER...BECAUSE OF THE 1840UNUSUALLY LARGE WIND FIELD...RAPID INTENSIFICATION IS NOT EXPECTED. 1841 1842ISAAC REMAINS A LARGE TROPICAL CYCLONE. A DANGEROUS STORM 1843SURGE...HEAVY RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE 1844CENTER AND ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN 1845GULF COAST. FOR THIS REASON...IT IS IMPORTANT NOT TO FOCUS ON THE 1846EXACT CENTER LOCATION. THE THREAT OF HEAVY RAINFALL AND FLOODING IS 1847ALSO EXPECTED TO SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY 1848REGION DURING THE NEXT FEW DAYS. 1849 1850FORECAST POSITIONS AND MAX WINDS 1851 1852INIT 28/2100Z 28.7N 89.2W 70 KT 80 MPH 1853 12H 29/0600Z 29.4N 90.0W 70 KT 80 MPH...INLAND 1854 24H 29/1800Z 30.3N 91.0W 55 KT 65 MPH...INLAND 1855 36H 30/0600Z 31.3N 91.9W 35 KT 40 MPH...INLAND 1856 48H 30/1800Z 33.0N 92.5W 30 KT 35 MPH...INLAND 1857 72H 31/1800Z 36.0N 92.5W 20 KT 25 MPH...INLAND 1858 96H 01/1800Z 39.0N 90.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 1859120H 02/1800Z 41.5N 86.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 1860 1861$$ 1862FORECASTER STEWART 1863 1864 1865WTNT44 KNHC 290252 1866TCDAT4 1867 1868HURRICANE ISAAC DISCUSSION NUMBER 32 1869NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 18701000 PM CDT TUE AUG 28 2012 1871 1872ISAAC PASSED OVER THE MISSISSIPPI RIVER DELTA IN EXTREME SOUTHEAST 1873LOUISIANA AROUND 2345 UTC. SINCE THAT TIME...THE CENTER HAS 1874WOBBLED WESTWARD AND HAS MOVED BACK OVER WATER. A NORTHWESTWARD 1875MOTION HAS RECENTLY RESUMED AND A SECOND LANDFALL SHOULD OCCUR 1876LATER TONIGHT NEAR GRAND ISLE. DATA FROM NOAA AND AIR FORCE 1877RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE MINIMUM 1878PRESSURE HAS CONTINUED TO GRADUALLY FALL AND IS NOW 968 MB. THE AIR 1879FORCE RESERVE AIRCRAFT HAS MEASURED A PEAK 850-MB FLIGHT-LEVEL WIND 1880OF 96 KT AND BIAS-CORRECTED SFMR WINDS OF AROUND 65 KT. BASED ON 1881THESE DATA...THE INITIAL INTENSITY REMAINS 70 KT. LITTLE CHANGE IN 1882STRENGTH IS EXPECTED DURING THE NEXT 12 HOURS OR SO AS THE CENTER 1883MOVES ACROSS THE BAYOUS OF SOUTHEASTERN LOUISIANA. STEADY 1884WEAKENING SHOULD COMMENCE LATER WEDNESDAY AS THE CENTER MOVES 1885FARTHER INLAND. 1886 1887SMOOTHING THROUGH THE WOBBLES DURING THE PAST FEW HOURS...THE LONGER 1888TERM MOTION ESTIMATE IS 310/7 KT. ISAAC IS EXPECTED TO MOVE SLOWLY 1889NORTHWESTWARD DURING THE NEXT 24 TO 36 HOURS AS A MID-LEVEL RIDGE TO 1890THE NORTHWEST OF THE CYCLONE SLIDES EASTWARD. AS THE RIDGE MOVES 1891ACROSS THE OHIO VALLEY AND INTO THE MID-ATLANTIC REGION...THIS 1892SHOULD CAUSE ISAAC TO TURN NORTH-NORTHWESTWARD AND NORTHWARD IN A 1893COUPLE OF DAYS. AFTER THAT TIME...THE CYCLONE IS EXPECTED TO TURN 1894NORTHEASTWARD AS IT ENTERS THE MID-LATITUDE WESTERLY FLOW. THE 1895GLOBAL MODEL GUIDANCE HAS BEEN SHIFTING WESTWARD DURING THE PAST 1896COUPLE OF RUNS...AND THE NHC FORECAST HAS BEEN ADJUSTED IN THAT 1897DIRECTION. 1898 1899BECAUSE OF THE SLOW MOTION OF ISAAC...A PROLONGED PERIOD OF STRONG 1900WINDS AND HEAVY RAINFALL ARE EXPECTED OVER A LARGE PORTION OF THE 1901NORTHERN GULF COAST. THE THREAT OF HEAVY RAINFALL AND FLOODING IS 1902ALSO EXPECTED TO SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY 1903REGION DURING THE NEXT FEW DAYS. 1904 1905NATIONAL OCEAN SERVICE TIDE GAUGES INDICATE THAT STORM SURGE HEIGHTS 1906OF 6 TO 10 FEET ARE OCCURRING ALONG PORTIONS OF THE COAST OF 1907SOUTHEASTERN LOUISIANA AND MISSISSIPPI. GIVEN THE LONG DURATION 1908OF ONSHORE FLOW IN THESE AREAS...WATER LEVELS ARE EXPECTED TO REMAIN 1909HIGH FOR THE NEXT 12 TO 24 HOURS. 1910 1911 1912FORECAST POSITIONS AND MAX WINDS 1913 1914INIT 29/0300Z 29.0N 89.7W 70 KT 80 MPH 1915 12H 29/1200Z 29.6N 90.6W 65 KT 75 MPH...INLAND 1916 24H 30/0000Z 30.3N 91.4W 55 KT 65 MPH...INLAND 1917 36H 30/1200Z 31.5N 92.3W 35 KT 40 MPH...INLAND 1918 48H 31/0000Z 33.2N 93.2W 25 KT 30 MPH...INLAND 1919 72H 01/0000Z 37.0N 94.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 1920 96H 02/0000Z 40.0N 91.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 1921120H 03/0000Z 41.5N 86.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 1922 1923$$ 1924FORECASTER BROWN 1925 1926 1927WTNT44 KNHC 290858 1928TCDAT4 1929 1930HURRICANE ISAAC DISCUSSION NUMBER 33 1931NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1932400 AM CDT WED AUG 29 2012 1933 1934AFTER REMAINING QUASI-STATIONARY FOR SEVERAL HOURS...AIRCRAFT AND 1935RADAR DATA INDICATE THAT THE CENTER OF ISAAC MADE A SECOND LANDFALL 1936NEAR PORT FOURCHON LOUISIANA AND IS BEGINNING TO MOVE INLAND OVER 1937SOUTHEAST LOUISIANA. OBSERVATIONS FROM THE HURRICANE HUNTER 1938AIRCRAFT INDICATE THAT THE EYE IS OPEN OVER THE WESTERN PORTION OF 1939THE CIRCULATION...AND THE RADAR PRESENTATION HAS BECOME MORE 1940ASYMMETRIC OVER THE PAST COUPLE OF HOURS. HOWEVER...THE RADAR 1941REFLECTIVITIES INDICATE THAT CONVECTION HAS BECOME STRONGER OVER 1942THE NORTHERN AND EASTERN PORTIONS OF THE CYCLONE...AND THE AIRCRAFT 1943REPORTED THAT THE CENTRAL PRESSURE REMAINS QUITE LOW. THE CURRENT 1944INTENSITY IS HELD AT 70 KT...BUT WEAKENING IS IMMINENT NOW THAT THE 1945CENTER HAS BEGUN TO MOVE OVER LAND. FOR THE NEXT 24 HOURS OR 1946SO...THE OFFICIAL INTENSITY FORECAST SHOWS A SOMEWHAT SLOWER RATE 1947OF WEAKENING THAN THAT GIVEN BY THE INLAND DECAY MODEL DUE TO THE 1948SWAMPY TERRAIN THAT THE SYSTEM WILL TRAVERSE. 1949 1950SINCE THE SYSTEM HAS ONLY BEGUN TO MOVE RECENTLY...THE INITIAL 1951MOTION IS AN UNCERTAIN 300/7. ISAAC IS CURRENTLY MOVING THROUGH A 1952WEAKNESS IN THE SUBTROPICAL RIDGE. OVER THE NEXT FEW DAYS...A 1953MID-LEVEL ANTICYLONE SHIFTS EASTWARD OVER THE CENTRAL AND EASTERN 1954UNITED STATES. AS A RESULT...ISAAC SHOULD GRADUALLY TURN TOWARD 1955THE NORTH AND NORTHEAST DURING THE FORECAST PERIOD. NEAR THE END 1956OF THE PERIOD...POST-TROPICAL ISAAC SHOULD MOVE EAST-NORTHEASTWARD 1957IN THE FLOW BETWEEN THE MID-LATITUDE WESTERLIES AND THE 1958AFOREMENTIONED ANTICYLONE. THE OFFICIAL TRACK FORECAST IS SIMILAR 1959TO THE PREVIOUS ONE AND CLOSE TO THE MODEL CONSENSUS. 1960 1961SINCE THE SYSTEM IS LIKELY TO MOVE SLOWLY OVER THE NEXT 24 HOURS OR 1962SO...THERE IS A CONTINUED THREAT OF FLOODING FROM HEAVY RAINS OVER 1963THE NORTHERN GULF COAST AREA. 1964 1965NATIONAL OCEAN SERVICE TIDE GAUGES INDICATE THAT STORM SURGE HEIGHTS 1966OF 6 TO 10 FEET ARE STILL OCCURRING ALONG PORTIONS OF THE COAST OF 1967SOUTHEASTERN LOUISIANA AND MISSISSIPPI. GIVEN THE LONG DURATION 1968OF ONSHORE FLOW IN THESE AREAS...WATER LEVELS ARE EXPECTED TO REMAIN 1969HIGH THROUGH TODAY. 1970 1971FORECAST POSITIONS AND MAX WINDS 1972 1973INIT 29/0900Z 29.2N 90.5W 70 KT 80 MPH...INLAND 1974 12H 29/1800Z 29.7N 91.1W 65 KT 75 MPH...INLAND 1975 24H 30/0600Z 30.5N 91.8W 50 KT 60 MPH...INLAND 1976 36H 30/1800Z 31.8N 92.8W 30 KT 35 MPH...INLAND 1977 48H 31/0600Z 33.6N 93.7W 25 KT 30 MPH...INLAND 1978 72H 01/0600Z 37.5N 93.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 1979 96H 02/0600Z 39.5N 90.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 1980120H 03/0600Z 40.5N 86.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 1981 1982$$ 1983FORECASTER PASCH/ROBERTS 1984 1985 1986WTNT44 KNHC 291451 1987TCDAT4 1988 1989HURRICANE ISAAC DISCUSSION NUMBER 34 1990NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 19911000 AM CDT WED AUG 29 2012 1992 1993HURRICANE ISAAC IS INLAND OVER SOUTHEASTERN LOUISIANA NEAR HOUMA. 1994THE CYCLONE HAS MAINTAINED AN IMPRESSIVE RADAR SIGNATURE...WHICH 1995INCLUDES A RAGGED 40-NMI DIAMETER EYE. CURVED CONVECTIVE RAINBANDS 1996HAVE INCREASED IN THE EASTERN SEMICIRCLE...AND DOPPLER RADAR 1997VELOCITIES OF NEAR 80 KT OVER WATER SUPPORT KEEPING ISAAC AS A 1998MINIMAL HURRICANE FOR THIS ADVISORY. SIMILAR DOPPLER VELOCITIES 1999OVER LAND AND OVER LAKE PONTCHARTRAIN SUGGEST WIND GUSTS TO NEAR 80 2000KT COULD OCCUR INLAND OVER SOUTHEASTERN LOUISIANA INTO THIS 2001AFTERNOON. BY LATE THIS AFTERNOON OR EVENING...HOWEVER...ISAAC IS 2002FORECAST TO WEAKEN TO A TROPICAL STORM...AND BECOME A TROPICAL 2003DEPRESSION BY THURSDAY NIGHT. 2004 2005THE INITIAL MOTION ESTIMATE IS 310/5. ISAAC IS EXPECTED TO MOVE 2006SLOWLY NORTHWESTWARD THROUGH A WEAKNESS IN THE SUBTROPICAL RIDGE 2007FOR THE NEXT 24 HOURS...AND THEN TURN NORTH-NORTHWESTWARD AND 2008NORTHWARD AROUND THE WESTERN PERIPHERY OF THE RIDGE BY 36 AND 48 2009HOURS...RESPECTIVELY. BY 72 HOURS...ISAAC IS FORECAST TO BECOME A 2010POST-TROPICAL REMNANT LOW PRESSURE SYSTEM THAT SHOULD MOVE 2011NORTHEASTWARD TO EAST-NORTHEASTWARD WHEN IT WILL BE CAUGHT UP IN 2012WEAK MID-LATITUDE WESTERLIES. THERE ARE CURRENTLY NO INDICATIONS IN 2013ANY OF THE MODEL GUIDANCE SUGGESTING THAT ISAAC WILL TAP INTO ANY 2014BAROCLINIC ENERGY SOURCES THAT COULD RESULT IN EXTRATROPICAL 2015STRENGTHENING OVER THE CENTRAL UNITED STATES. THE OFFICIAL TRACK 2016FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY TRACK AND IS JUST EAST 2017OF THE MODEL CONSENSUS. 2018 2019SINCE ISAAC IS FORECAST TO MOVE SLOWLY OVER THE NEXT 24-36 HOURS... 2020THERE WILL BE A PROLONGED THREAT OF FLOODING FROM HEAVY RAINS OVER 2021THE NORTHERN GULF COAST AREA AND THE SOUTH-CENTRAL UNITED STATES. 2022 2023NATIONAL OCEAN SERVICE TIDE GAGES INDICATE THAT STORM SURGE HEIGHTS 2024OF 6 TO 8 FEET ARE STILL OCCURRING ALONG PORTIONS OF THE COAST OF 2025SOUTHEASTERN LOUISIANA AND MISSISSIPPI. GIVEN THE LONG DURATION 2026OF ONSHORE FLOW IN THESE AREAS...WATER LEVELS ARE EXPECTED TO REMAIN 2027HIGH THROUGH TODAY. 2028 2029A SPECIAL THANKS TO THE CREWS OF THE AIR FORCE RESERVE AND NOAA 2030HURRICANE HUNTERS WHO FLEW A TOTAL OF 34 HAZARDOUS MISSIONS INTO 2031ISAAC...WHICH RESULTED IN AN IMPRESSIVE TOTAL OF 95 CENTER FIXES. 2032 2033FORECAST POSITIONS AND MAX WINDS 2034 2035INIT 29/1500Z 29.6N 90.7W 65 KT 75 MPH...INLAND 2036 12H 30/0000Z 30.2N 91.4W 55 KT 65 MPH...INLAND 2037 24H 30/1200Z 31.2N 92.2W 45 KT 50 MPH...INLAND 2038 36H 31/0000Z 32.8N 93.1W 30 KT 35 MPH...INLAND 2039 48H 31/1200Z 34.6N 93.5W 25 KT 30 MPH...INLAND 2040 72H 01/1200Z 38.0N 92.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 2041 96H 02/1200Z 40.0N 89.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2042120H 03/1200Z 41.0N 85.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2043 2044$$ 2045FORECASTER STEWART 2046 2047 2048WTNT44 KNHC 292056 2049TCDAT4 2050 2051TROPICAL STORM ISAAC DISCUSSION NUMBER 35 2052NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 2053400 PM CDT WED AUG 29 2012 2054 2055ISAAC CONTINUES TO TRUDGE SLOWLY TO THE NORTHWEST ACROSS 2056SOUTHEASTERN LOUISIANA...AND THE INITIAL MOTION REMAINS 310/5 2057KT...BASED ON DOPPLER RADAR DATA FROM SLIDELL AND FT. POLK 2058LOUISIANA. THE MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT WITH 2059THE PREVIOUS OFFICIAL TRACK...SO NO SIGNIFICANT CHANGES WERE MADE 2060FOR THIS ADVISORY. ISAAC SHOULD CONTINUE TO MOVE NORTHWESTWARD AND 2061EVENTALLY NORTHWARD THROUGH A WEAKNESS IN THE SUBTROPICAL RIDGE 2062OVER THE NEXT 36-48 HOURS. BY DAY 3 WHEN THE REMNANT CYCLONE IS 2063OVER THE UPPER-MIDWEST...ISAAC SHOULD TURN EAST-NORTHEASTWARD WHEN 2064IT INTERACTS WITH WEAK MID-LATITUDE WESTERLY FLOW. THE OFFICIAL 2065FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS ADVISORY 2066TRACK...AND LIES BETWEEN THE MODEL CONSENSUS AND THE ECMWF MODEL. 2067 2068STRONG BANDS OF THUNDERSTORMS CONTINUE TO DEVELOP OVER WATER IN THE 2069THE EASTERN SEMICIRCLE AND ALSO SOUTHWEST OF THE CENTER. THEY HAVE 2070OCCASIONALLY PRODUCED SUSTAINED TROPICAL-STORM-FORCE WINDS ALONG 2071WITH GUSTS EXCEEDING 60 KT. THOSE STRONG RAINBANDS WILL GRADUALLY 2072SPREAD WESTWARD TONIGHT ACROSS THE COASTAL AREAS OF SOUTHEASTERN 2073LOUISIANA AND SOUTHERN MISSISSIPPI...INCLUDING THE NEW ORLEANS 2074METROPOLITAN AREA. BY THURSDAY NIGHT...ISAAC COULD WEAKEN TO A 2075TROPICAL DEPRESSION...AND IT SHOULD BECOME A POST-TROPICAL REMNANT 2076LOW PRESSURE SYSTEM BY FRIDAY. THERE REMAINS NO INDICATION IN ANY 2077OF THE NHC MODEL GUIDANCE THAT ISAAC WILL BE ABLE TO ACQUIRE ANY 2078BAROCLINIC ENERGY THAT COULD CAUSE IT TO STRENGTHEN INTO A 2079SIGNIFICANT EXTRATROPICAL LOW WHILE IT IS OVER THE UNITED STATES. 2080 2081SINCE ISAAC WILL CONTINUE TO MOVE SLOWLY OVER THE NEXT 24-36 2082HOURS...THERE WILL BE A PROLONGED THREAT OF FLOODING FROM HEAVY 2083RAINS OVER THE NORTHERN GULF COAST AREA AND THE SOUTH-CENTRAL 2084UNITED STATES. 2085 2086NATIONAL OCEAN SERVICE TIDE GAGES INDICATE THAT STORM SURGE HEIGHTS 2087OF NEAR 7 FEET ARE STILL OCCURRING ALONG PORTIONS OF THE COAST OF 2088SOUTHEASTERN LOUISIANA AND MISSISSIPPI. GIVEN THE LONG DURATION 2089OF ONSHORE FLOW IN THESE AREAS...WATER LEVELS ARE EXPECTED TO REMAIN 2090HIGH THROUGH TONIGHT. 2091 2092PUBLIC ADVISORY TIMES HAVE REVERTED BACK TO A 3-HOURLY CYCLE. THE 2093NEXT INTERMEDIATE PUBLIC ADVISORY WILL BE ISSUED AT 700 PM 2094CDT/0000Z. 2095 2096FORECAST POSITIONS AND MAX WINDS 2097 2098INIT 29/2100Z 30.0N 91.1W 60 KT 70 MPH...INLAND 2099 12H 30/0600Z 30.7N 91.7W 50 KT 60 MPH...INLAND 2100 24H 30/1800Z 32.0N 92.6W 40 KT 45 MPH...INLAND 2101 36H 31/0600Z 33.8N 93.3W 30 KT 35 MPH...INLAND 2102 48H 31/1800Z 35.7N 93.4W 25 KT 30 MPH...INLAND 2103 72H 01/1800Z 38.6N 91.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 2104 96H 02/1800Z 40.0N 88.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2105120H 03/1800Z 40.5N 83.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 2106 2107$$ 2108FORECASTER STEWART 2109 2110 2111WTNT44 KNHC 300255 2112TCDAT4 2113 2114TROPICAL STORM ISAAC DISCUSSION NUMBER 36 2115NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 21161000 PM CDT WED AUG 29 2012 2117 2118NATIONAL WEATHER SERVICE DOPPLER RADAR IMAGERY SHOWS THAT ISAAC 2119CONTINUES TO MOVE SLOWLY NORTHWESTWARD AT ABOUT 5 KT OVER 2120SOUTHEASTERN LOUISIANA. THE SLOW FORWARD SPEED IS EXPECTED TO 2121PERSIST OVERNIGHT. HOWEVER...A SLIGHT INCREASE IS FORWARD SPEED 2122AND A TURN TOWARD THE NORTH-NORTHWEST SHOULD OCCUR ON THURSDAY 2123AS ISAAC MOVES AROUND THE WESTERN PERIPHERY OF A RIDGE THAT MOVES 2124EASTWARD INTO THE MID-ATLANTIC REGION. IN 2 TO 3 DAYS...THE 2125CYCLONE SHOULD TURN NORTHEASTWARD...THEN EASTWARD AS IT ENTERS AN 2126AREA OF WEAK MID-LATITUDE WESTERLY FLOW. THE OFFICIAL FORECAST IS 2127CLOSE TO THE PREVIOUS TRACK THROUGH 36 HOURS...BUT IS ADJUSTED 2128SLIGHTLY WEST AT 48 AND 72 HOURS TO BE CLOSER TO THE LATEST 2129GUIDANCE. 2130 2131RECENT WIND OBSERVATIONS NEAR THE NORTHERN GULF COAST INDICATE 2132THAT THE MAXIMUM WINDS ARE ABOUT 50 KT. THESE WINDS ARE PRIMARILY 2133OCCURRING OVER WATER. CONTINUED WEAKENING IS EXPECTED AND ISAAC 2134SHOULD BECOME A TROPICAL DEPRESSION BY THURSDAY EVENING. 2135 2136HEAVY RAINFALL AND A SIGNIFICANT FLOOD THREAT ARE EXPECTED TO SPREAD 2137INLAND ACROSS PORTIONS OF THE CENTRAL UNITED STATES DURING THE NEXT 2138SEVERAL DAYS. WATER LEVELS ALONG THE NORTHERN GULF COAST WILL 2139REMAIN ELEVATED THROUGH EARLY THURSDAY. 2140 2141 2142FORECAST POSITIONS AND MAX WINDS 2143 2144INIT 30/0300Z 30.3N 91.2W 50 KT 60 MPH 2145 12H 30/1200Z 31.2N 92.0W 40 KT 45 MPH...INLAND 2146 24H 31/0000Z 32.8N 92.9W 30 KT 35 MPH...INLAND 2147 36H 31/1200Z 34.9N 93.6W 25 KT 30 MPH...INLAND 2148 48H 01/0000Z 37.3N 93.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 2149 72H 02/0000Z 39.5N 91.3W 15 KT 15 MPH...POST-TROP/REMNT LOW 2150 96H 03/0000Z 40.0N 87.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2151120H 04/0000Z 40.5N 83.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2152 2153$$ 2154FORECASTER BROWN 2155 2156 2157WTNT44 KNHC 300852 2158TCDAT4 2159 2160TROPICAL STORM ISAAC DISCUSSION NUMBER 37 2161NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 2162400 AM CDT THU AUG 30 2012 2163 2164ISAAC IS SLOWLY WEAKENING AS MORE OF ITS LARGE CIRCULATION MOVES 2165OVER LAND. BASED ON THE LATEST SURFACE WIND OBSERVATIONS NEAR THE 2166NORTHERN GULF COAST...THE MAXIMUM WINDS HAVE DIMINISHED TO NEAR 40 2167KT. THESE WINDS ARE OCCURRING PRIMARILY OVER WATER OR ALONG THE 2168COASTLINE. CONTINUED GRADUAL WEAKENING IS EXPECTED...AND ISAAC IS 2169LIKELY TO BECOME A TROPICAL DEPRESSION BY THIS EVENING. THE 2170OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ONE...AND IS 2171MORE OR LESS IN AGREEMENT WITH THE STATISTICAL-DYNAMICAL GUIDANCE. 2172 2173CENTER FIXES USING SURFACE SYNOPTIC DATA AND NATIONAL WEATHER 2174SERVICE DOPPLER RADAR IMAGERY INDICATE THAT ISAAC IS MOVING 2175NORTHWESTWARD AT A SLIGHTLY FASTER PACE...325/7. THE TRACK 2176FORECAST AND PROGNOSTIC REASONING REMAIN ESSENTIALLY UNCHANGED. 2177OVER THE NEXT SEVERAL DAYS...THE PRIMARY STEERING MECHANISM SHOULD 2178BE THE FLOW BETWEEN THE MID-LATITUDE WESTERLIES AND A RIDGE OVER 2179THE SOUTHEASTERN UNITED STATES. AS A RESULT THE CYCLONE IS 2180EXPECTED TO TURN NORTHWARD...NORTHEASTWARD...AND EASTWARD DURING 2181THE FORECAST PERIOD. THE OFFICIAL TRACK FORECAST IS VERY CLOSE TO 2182THE PREVIOUS ONE...AND ALSO CLOSE TO THE LATEST DYNAMICAL MODEL 2183CONSENSUS. 2184 2185HEAVY RAINFALL AND A SIGNIFICANT FLOOD THREAT ARE EXPECTED TO SPREAD 2186INLAND ACROSS PORTIONS OF THE CENTRAL UNITED STATES DURING THE NEXT 2187SEVERAL DAYS. WATER LEVELS ALONG THE NORTHERN GULF COAST WILL 2188REMAIN ELEVATED THROUGH AT LEAST THIS MORNING. TORNADOES REMAIN A 2189THREAT AS WELL FROM THIS SYSTEM TODAY. 2190 2191FORECAST POSITIONS AND MAX WINDS 2192 2193INIT 30/0900Z 30.9N 91.6W 40 KT 45 MPH 2194 12H 30/1800Z 31.9N 92.3W 35 KT 40 MPH...INLAND 2195 24H 31/0600Z 33.8N 93.2W 30 KT 35 MPH...INLAND 2196 36H 31/1800Z 36.0N 93.5W 25 KT 30 MPH...INLAND 2197 48H 01/0600Z 38.0N 93.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 2198 72H 02/0600Z 39.5N 90.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2199 96H 03/0600Z 40.0N 86.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 2200120H 04/0600Z 40.5N 82.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2201 2202$$ 2203FORECASTER PASCH 2204 2205 2206WTNT44 KNHC 301441 2207TCDAT4 2208 2209TROPICAL STORM ISAAC DISCUSSION NUMBER 38 2210NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 22111000 AM CDT THU AUG 30 2012 2212 2213CENTER FIXES USING SURFACE OBSERVATIONS AND NOAA DOPPLER WEATHER 2214RADARS INDICATE THAT ISAAC IS MOVING NORTHWESTWARD AT 330/08 KT. 2215THE FORECAST TACK AND REASONING REMAIN BASICALLY UNCHANGED FROM THE 2216PREVIOUS ADVISORY. ISAAC AND ITS REMNANTS ARE EXPECTED TO BE 2217STEERED NORTHWARD AROUND THE WESTERN PORTION OF A SUBTROPICAL RIDGE 2218THAT IS LOCATED OVER THE SOUTHEASTERN U.S. THROUGH DAY 2...AND THEN 2219TURN NORTHEASTWARD AND EASTWARD ON DAY 3-5 AS THE SYSTEM MOVES INTO 2220WEAK MID-LATITUDE WESTERLY FLOW. THE OFFICIAL TRACK FORECAST IS 2221VERY CLOSE TO THE PREVIOUS ONE...AND LIES CLOSE TO THE LATEST 2222DYNAMICAL MODEL CONSENSUS. 2223 2224THE INITIAL INTENSITY HAS BEEN DECREASED TO 35 KT...AND THAT IS IN 2225SMALL AREA OVER WATER BETWEEN SOUTHEASTERN LOUISIANA AND THE 2226MISSISSIPPI COAST...AND PERHAPS EXTENDING A FEW MILES INLAND. 2227ISAAC WILL CONTINUE TO WEAKEN OVER LAND AND IT IS LIKELY TO BECOME A 2228TROPICAL DEPRESSION BY THIS EVENING...AND BECOME A POST-TROPICAL 2229REMNANT LOW BY SATURDAY...IF NOT SOONER. THE OFFICIAL INTENSITY 2230FORECAST IS SIMILAR TO THE PREVIOUS ONE...AND CLOSELY FOLLOWS THE 2231DECAY-SHIPS STATISTICAL-DYNAMICAL INTENSITY MODEL. 2232 2233HEAVY RAINFALL AND A SIGNIFICANT FLOOD THREAT WILL CONTINUE TO 2234SPREAD INLAND ACROSS PORTIONS OF THE CENTRAL UNITED STATES DURING 2235THE NEXT SEVERAL DAYS. WATER LEVELS ALONG THE NORTHERN GULF COAST 2236WILL REMAIN ELEVATED THROUGH AT LEAST THIS MORNING. THE THREAT FOR 2237TORNADOES WITH THIS SYSTEM ALSO APPEARS TO BE INCREASING TODAY. 2238 2239FORECAST POSITIONS AND MAX WINDS 2240 2241INIT 30/1500Z 31.7N 92.1W 35 KT 40 MPH...INLAND 2242 12H 31/0000Z 33.0N 92.8W 30 KT 35 MPH...INLAND 2243 24H 31/1200Z 35.0N 93.3W 25 KT 30 MPH...INLAND 2244 36H 01/0000Z 37.0N 93.3W 20 KT 25 MPH...INLAND 2245 48H 01/1200Z 38.4N 92.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 2246 72H 02/1200Z 39.4N 89.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 2247 96H 03/1200Z 39.5N 86.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2248120H 04/1200Z 39.5N 83.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 2249 2250$$ 2251FORECASTER STEWART 2252 2253 2254WTNT44 KNHC 302048 2255TCDAT4 2256 2257TROPICAL DEPRESSION ISAAC DISCUSSION NUMBER 39 2258NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 2259400 PM CDT THU AUG 30 2012 2260 2261SURFACE OBSERVATIONS AND NOAA DOPPLER WEATHER RADARS INDICATE THAT 2262ISAAC IS MOVING NORTH-NORTHWESTWARD AT 340/11 KT. ISAAC WILL 2263GRADUALLY TURN TO THE NORTH OVER THE NEXT 24-36 HOURS...AND MOVE 2264ACROSS ARKANSAS AND INTO MISSOURI. BY DAY 3...THE REMNANTS OF ISAAC 2265SHOULD TURN NORTHEASTWARD AND THEN EASTWARD AS THE SYSTEM MOVES 2266INTO WEAK MID-LATITUDE WESTERLY FLOW. THE OFFICIAL TRACK FORECAST 2267IS VERY CLOSE TO THE PREVIOUS ONE...AND LIES JUST TO THE RIGHT OF 2268THE CONSENSUS MODELS TCVA AND TV15. 2269 2270THE INITIAL INTENSITY HAS BEEN DECREASED TO 30 KT...BASED ON SURFACE 2271OBSERVATIONS AND DOPPLER RADAR VELOCITY DATA. ISAAC WILL CONTINUE 2272TO WEAKEN OVER LAND AND IT IS EXPECTED TO BECOME A POST-TROPICAL 2273REMNANT LOW BY SATURDAY...IF NOT SOONER. THE OFFICIAL INTENSITY 2274FORECAST IS SIMILAR TO THE PREVIOUS ONE...AND CLOSELY FOLLOWS THE 2275DECAY-SHIPS STATISTICAL-DYNAMICAL INTENSITY MODEL. 2276 2277HEAVY RAINFALL AND A SIGNIFICANT FLOOD THREAT WILL CONTINUE TO 2278SPREAD INLAND ACROSS PORTIONS OF THE CENTRAL UNITED STATES DURING 2279THE NEXT SEVERAL DAYS. WATER LEVELS ALONG THE NORTHERN GULF COAST 2280WILL REMAIN ELEVATED THROUGH THIS EVENING...AND THEN GRADUALLY 2281SUBSIDE ON FRIDAY. THE THREAT FOR TORNADOES WITH THIS SYSTEM WILL 2282CONTINUE THROUGH TONIGHT. 2283 2284THIS IS THE LAST ADVISORY ON ISAAC ISSUED BY THE NATIONAL HURRICANE 2285CENTER. FUTURE INFORMATION ON THIS SYSTEM CAN BE FOUND IN PUBLIC 2286ADVISORIES ISSUED BY THE HYDROMETEOROLOGICAL PREDICTION CENTER... 2287UNDER AWIPS HEADER TCPAT4 AND WMO HEADER WTNT34 KWNH...BEGINNING AT 228810 PM CDT. 2289 2290FORECAST POSITIONS AND MAX WINDS 2291 2292INIT 30/2100Z 32.7N 92.6W 30 KT 35 MPH...INLAND 2293 12H 31/0600Z 34.0N 93.0W 25 KT 30 MPH...INLAND 2294 24H 31/1800Z 36.0N 93.2W 20 KT 25 MPH...INLAND 2295 36H 01/0600Z 37.7N 92.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 2296 48H 01/1800Z 38.6N 91.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 2297 72H 02/1800Z 39.5N 88.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 2298 96H 03/1800Z 39.5N 85.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 2299120H 04/1800Z 38.5N 82.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 2300 2301$$ 2302FORECASTER STEWART 2303 2304 2305