WTNT42 KNHC 050236 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 PM AST WED SEP 04 2013 THE SATELLITE PRESENTATION OF THE CYCLONE CONSISTS OF A SMALL AREA OF VERY DEEP CONVECTION NEAR AND NORTHEAST OF THE SURFACE CENTER WHILE THE CONVECTIVE BANDS HAVE LARGELY DISSIPATED OVER THE PAST FEW HOURS. THE LARGE-SCALE OUTFLOW PATTERN OVER THE CYCLONE IS EXCELLENT WITH AN ENHANCED POLEWARD OUTFLOW CHANNEL SEEN IN WATER VAPOR IMAGERY. BASED ON THE LATEST SATELLITE CLASSIFICATIONS FROM BOTH TAFB AND SAB...THE INITIAL INTENSITY IS SET TO 35 KT...AND THE DEPRESSION IS NOW TROPICAL STORM GABRIELLE. DROPSONDE DATA FROM THE NASA GLOBAL HAWK AIRCRAFT SUGGEST THAT THE CIRCULATION OF GABRIELLE IS TILTED TO THE NORTHEAST WITH HEIGHT... WITH A MID-LEVEL CIRCULATION SEEN IN DATA FROM THE SAN JUAN WSR-88D RADAR. THIS TILTED STRUCTURE IS CONSISTENT WITH SOUTHERLY TO SOUTHWESTERLY VERTICAL SHEAR OF 5 TO 10 KT SHOWN OVER THE CYCLONE BY THE UW-CIMSS AND SHIPS MODEL ANALYSES. IN ADDITION...THE DROPSONDE DATA SHOWED DRY AIR IN THE MID LEVELS OF THE ATMOSPHERE AROUND GABRIELLE. GIVEN THE ENVIRONMENT...THE SOMEWHAT DISORGANIZED STATE OF THE CIRCULATION...POSSIBLE LAND INTERACTION...AND THE PRESENCE OF THE LARGE AREA OF DISTURBED WEATHER NORTHEAST OF GABRIELLE...NOT MUCH STRENGTHENING IS EXPECTED IN THE SHORT TERM. THE NHC FORECAST IS IN GOOD AGREEMENT WITH THE INTENSITY CONSENSUS AIDS FOR THE FIRST 24 HOURS. IT IS ENTIRELY POSSIBLE THAT THE LOW-LEVEL CIRCULATION WILL DISSIPATE IN THE NEXT 24 HOURS. ASSUMING THAT GABRIELLE SURVIVES...ONLY LIMITED INTENSIFICATION IS SHOWN LATER IN THE PERIOD AS THE SHEAR INCREASES DRAMATICALLY AHEAD OF AN UPPER-LEVEL TROUGH. THE NHC FORECAST REMAINS BELOW MUCH OF THE INTENSITY GUIDANCE LATE IN THE PERIOD...WHICH SEEMS TOO HIGH GIVEN THE INCREASE IN SHEAR. THE NHC FORECAST IS ALSO SUPPORTED BY THE GLOBAL MODELS...WHICH DO NOT SHOW MUCH INTENSIFICATION AFTER GABRIELLE MOVES NORTH OF THE CARIBBEAN SEA. THE LOW-LEVEL CENTER HAS BEEN DIFFICULT TO LOCATE...BUT THE GLOBAL HAWK DROPSONDE DATA SUGGEST IT REMAINS SOUTHWEST OF THE MID-LEVEL CENTER SEEN IN RADAR IMAGERY. GIVEN THE DIFFICULTY LOCATING THE CENTER...THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 320/7. THE SYNOPTIC-SCALE TRACK REASONING HAS NOT CHANGED...AS GABRIELLE IS EXPECTED TO MOVE GENERALLY NORTHWESTWARD DURING THE NEXT DAY OR SO...FOLLOWED A TURN TOWARD THE NORTH BY 72 HOURS AS THE CYCLONE MOVES AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. LATE IN THE PERIOD AN ACCELERATION TOWARD THE NORTHEAST IS EXPECTED AHEAD OF AN UPPER-LEVEL TROUGH OVER THE WESTERN ATLANTIC. THE NHC TRACK FORECAST IS LARGELY AN UPDATE OF THE PREVIOUS ONE THROUGH 72 HOURS AND LIES A LITTLE TO THE RIGHT OF MOST OF THE MODEL GUIDANCE DURING THIS PERIOD. AT DAYS 4 AND 5 THE NHC FORECAST IS A LITTLE TO THE RIGHT OF THE PREVIOUS ONE AND IS CLOSE TO THE GFS ENSEMBLE MEAN AND FSU SUPERENSEMBLE. REGARDLESS OF THE EXACT TRACK OF THE CENTER OF GABRIELLE DURING THE NEXT 24 HOURS...THE MAIN THREAT WILL BE HEAVY RAINFALL OVER PORTIONS OF PUERTO RICO AND THE DOMINICAN REPUBLIC. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 17.0N 66.6W 35 KT 40 MPH 12H 05/1200Z 17.8N 67.4W 40 KT 45 MPH 24H 06/0000Z 19.0N 68.4W 45 KT 50 MPH 36H 06/1200Z 20.1N 69.0W 45 KT 50 MPH 48H 07/0000Z 21.2N 69.4W 45 KT 50 MPH 72H 08/0000Z 23.3N 69.2W 50 KT 60 MPH 96H 09/0000Z 25.5N 67.5W 50 KT 60 MPH 120H 10/0000Z 29.5N 63.9W 50 KT 60 MPH $$ FORECASTER BRENNAN WTNT42 KNHC 050841 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST THU SEP 05 2013 ALTHOUGH THE AREA OF DEEP CONVECTION HAS EXPANDED SIGNIFICANTLY DURING THE PAST SEVERAL HOURS AND THE OUTFLOW IS EXCELLENT... SURROUNDING SURFACE OBSERVATIONS DO NOT SUGGEST THAT THERE HAS BEEN ANY IMPROVEMENT OF THE CIRCULATION. IN ADDITION...MICROWAVE OR DOPPLER RADAR DATA DO NOT SHOW ANY DEVELOPMENT OF AN INNER CORE...ALTHOUGH RADAR IMAGES SHOW A WELL-DEFINED MID-LEVEL CENTER TO THE EAST OF THE SURFACE LOCATION. I WOULD NOT BE SURPRISED IF THERE IS A REFORMATION OF THE SURFACE CENTER. A RECONNAISSANCE PLANE LATER THIS MORNING WILL HELP US TO DETERMINE IF THIS IS THE CASE. SUBJECTIVE ESTIMATES FROM TAFB AND SAB AS WELL AS OBJECTIVE ESTIMATES FROM THE UNIVERSITY OF WISCONSIN...CIMSS...ARE 2.5 ON THE DVORAK SCALE. ON THIS BASIS...THE INITIAL INTENSITY IS KEPT AT 35 KNOTS...AND THESE WINDS ARE PROBABLY CONFINED TO A VERY SMALL AREA NEAR THE CENTER. THE INTENSITY FORECAST IS HIGHLY UNCERTAIN. MOST OF THE GLOBAL MODELS KEEP A WEAK CYCLONE FOR A FEW DAYS WITH THE EXCEPTION OF THE ECMWF WHICH DISSIPATES GABRIELLE JUST NORTH OF HISPANIOLA IN A COUPLE OF DAYS. GIVEN THE STRONG WESTERLY SHEAR WHICH IS FORECAST TO BECOME ESTABLISHED ALONG THE FORECAST PATH OF GABRIELLE...THE DISSIPATION OPTION OF THE ECMWF IS NOT OUT OF THE QUESTION. AT THIS TIME...THE NHC FORECAST FOLLOWS THE MODEL CONSENSUS SHOWING SOME SLIGHT STRENGTHENING GIVING CREDIT TO THE OTHER MODELS. ALTHOUGH THE SURFACE CENTER IS DIFFICULT TO FIND ON IR IMAGES...IT APPEARS TO BE ON THE WESTERN EDGE OF THE DEEP CONVECTION. THE BEST ESTIMATE OF THE INITIAL MOTION IS TOWARD THE NORTHWEST OR 320 DEGREES AT 7 KNOTS. GABRIELLE IS EMBEDDED WITHIN A WEAK STEERING FLOW SOUTH OF A NARROW RIDGE OF HIGH PRESSURE OVER THE WESTERN ATLANTIC. IN A DAY OR TWO...A MID-LEVEL TROUGH IS FORECAST TO MOVE FROM THE UNITED STATES EASTWARD ACROSS THE ATLANTIC...CAUSING GABRIELLE TO RECURVE AND MOVE TOWARD THE OPEN ATLANTIC. THE OFFICIAL FORECAST IS VERY CLOSE TO THE MULTI-MODEL CONSENSUS AND IS NOT TOO DIFFERENT FROM THE PREVIOUS ONE. REGARDLESS OF THE EXACT TRACK OF THE CENTER OF GABRIELLE DURING THE NEXT 24 HOURS...THE MAIN THREAT WILL BE HEAVY RAINFALL OVER PORTIONS OF PUERTO RICO AND THE EASTERN PORTION OF THE DOMINICAN REPUBLIC. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 17.5N 66.9W 35 KT 40 MPH 12H 05/1800Z 18.5N 67.7W 35 KT 40 MPH 24H 06/0600Z 19.7N 68.5W 40 KT 45 MPH 36H 06/1800Z 20.9N 69.1W 45 KT 50 MPH 48H 07/0600Z 21.8N 69.5W 50 KT 60 MPH 72H 08/0600Z 24.0N 69.0W 50 KT 60 MPH 96H 09/0600Z 27.0N 66.0W 50 KT 60 MPH 120H 10/0600Z 31.5N 62.5W 50 KT 60 MPH $$ FORECASTER AVILA WTNT42 KNHC 051441 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 AM AST THU SEP 05 2013 A COMBINATION OF SATELLITE...SAN JUAN DOPPLER RADAR...RAWINSONDE... AND AIRCRAFT DATA INDICATES THAT GABRIELLE HAS BECOME VERY DISORGANIZED. THE LOW-LEVEL CENTER...WHICH IS POORLY DEFINED...IS LOCATED SOUTH OF THE MONA PASSAGE ABOUT 130 N MI FROM THE MID-LEVEL CENTER THAT IS LOCATED BETWEEN PUERTO RICO AND THE VIRGIN ISLANDS. THIS STRUCTURE MAY BE DUE TO SOME WESTERLY VERTICAL WIND SHEAR... ALTHOUGH THE SHEAR APPEARS TO BE TOO LIGHT TO HAVE SUCH A DRASTIC EFFECT ON THE CYCLONE. NONE OF THE DATA CURRENTLY SUGGEST TROPICAL STORM FORCE WINDS ARE OCCURRING...SO GABRIELLE IS DOWNGRADED TO A 30-KT TROPICAL DEPRESSION. CONVECTION CONTINUES NEAR THE MID-LEVEL CENTER...SO THERE IS STILL A CHANCE OF THE LOW-LEVEL CENTER REFORMING IN THAT AREA. IF THAT DOES NOT OCCUR...GABRIELLE IS EXPECTED TO WEAKEN AS IT INTERACTS WITH THE TERRAIN OF THE DOMINICAN REPUBLIC AND ENCOUNTERS INCREASING WESTERLY SHEAR. THE REVISED INTENSITY FORECAST NOW CALLS FOR THE CYCLONE TO DEGENERATE TO A REMNANT LOW PRESSURE AREA IN 24 HOURS AND TO DISSIPATE COMPLETELY THEREAFTER. THE INITIAL MOTION IS AN UNCERTAIN 305/8. LOW-LEVEL RIDGING NORTH AND NORTHEAST OF GABRIELLE SHOULD ALLOW THIS GENERAL MOTION TO CONTINUE UNTIL THE CYCLONE DISSIPATES. IF THE SYSTEM SURVIVES LONGER THAN CURRENTLY FORECAST...THE DYNAMICAL MODELS SUGGEST IT WILL TURN NORTHWARD IN RESPONSE TO A DEVELOPING DEEP-LAYER TROUGH OVER THE WESTERN ATLANTIC. A HEAVY RAIN THREAT CONTINUES OVER PUERTO RICO AND THE VIRGIN ISLANDS. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 17.5N 68.1W 30 KT 35 MPH 12H 06/0000Z 18.3N 68.8W 25 KT 30 MPH 24H 06/1200Z 19.6N 69.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 07/0000Z...DISSIPATED $$ FORECASTER BEVEN WTNT42 KNHC 052036 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 PM AST THU SEP 05 2013 GABRIELLE IS BEING GENEROUSLY MAINTAINED AS A TROPICAL CYCLONE AT THIS TIME...AS THERE IS JUST ENOUGH OF A CIRCULATION AND ORGANIZED CONVECTION TO KEEP IT FROM BEING DECLARED A REMNANT LOW. THE CYCLONE REMAINS VERY BADLY ORGANIZED...WITH THE LOW-LEVEL CENTER NOW SEPARATED FROM THE MID-LEVEL CENTER BY ABOUT 180 N MI. THE INITIAL INTENSITY IS REDUCED TO 25 KT BASED ON EARLIER SCATTEROMETER DATA...AND THE CENTRAL PRESSURE IS NEAR 1010 MB BASED ON MULTIPLE SURFACE OBSERVATIONS. WHILE CONVECTION CONTINUES NEAR THE MID-LEVEL CENTER...THERE ARE NO SIGNS AT THIS TIME THAT THE LOW-LEVEL CENTER IS TRYING TO RE-FORM THERE. IF THAT DOES NOT OCCUR...GABRIELLE IS EXPECTED TO DEGENERATE TO A REMNANT LOW PRESSURE AREA AS IT INTERACTS WITH THE TERRAIN OF THE DOMINICAN REPUBLIC...ENCOUNTERS INCREASING WESTERLY SHEAR...AND MOVES INTO A DRIER AIR MASS. THE INTENSITY FORECAST CONTINUES TO CALL FOR THE CYCLONE TO COMPLETELY DISSIPATE AFTER 24 HOURS. IT SHOULD BE NOTED THAT THE DYNAMICAL MODELS FORECAST A LOW PRESSURE AREA TO DEVELOP SOUTH OR SOUTHWEST OF BERMUDA DURING THE NEXT 2-4 DAYS. WHETHER THIS WILL VERIFY...AND WHETHER THE LOW DEVELOPS FROM THE REMNANTS OF GABRIELLE OR FROM ANOTHER DISTURBANCE TO ITS NORTHEAST...IS UNCLEAR AT THIS TIME. THE INITIAL MOTION REMAINS 305/8. LOW-LEVEL RIDGING NORTH AND NORTHEAST OF GABRIELLE SHOULD ALLOW A MOTION TOWARD THE NORTHWEST OR NORTH-NORTHWEST TO OCCUR UNTIL THE CYCLONE DISSIPATES. A HEAVY RAIN THREAT CONTINUES OVER PUERTO RICO AND THE VIRGIN ISLANDS. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 18.2N 68.6W 25 KT 30 MPH 12H 06/0600Z 19.2N 69.3W 25 KT 30 MPH 24H 06/1800Z 20.8N 70.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 07/0600Z...DISSIPATED $$ FORECASTER BEVEN WTNT42 KNHC 100845 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST TUE SEP 10 2013 DURING THE PAST 12 HOURS...INFRARED SATELLITE IMAGERY INDICATES DEEP CONVECTION HAS DEVELOPED AND PERSISTED OVER AND TO THE EAST OF THE WELL-DEFINED LOW-LEVEL CIRCULATION CENTER ASSOCIATED WITH THE REMNANTS OF GABRIELLE. IN ADDITION...AN EARLIER ASCAT OVERPASS CONTAINED SOME 34- TO 36-KT WIND VECTORS TO THE SOUTH OF THE CENTER AND OBSERVATIONS FROM NOAA BUOY 41049 LOCATED MORE THAN 100 NMI SOUTHEAST OF THE CENTER HAVE BEEN STEADILY INCREASING TO AT LEAST 31 KT OUTSIDE OF CONVECTION. BASED ON THE ABOVE DATA...ADVISORIES HAVE BEEN RE-INITIATED ON TROPICAL STORM GABRIELLE. AN AIR FORCE RESERVE AIRCRAFT IS SCHEDULED TO RECONNOITER THE CYCLONE THIS AFTERNOON TO PROVIDE MORE DETAILED INFORMATION ON THE EXACT LOCATION AND STRENGTH OF GABRIELLE. THE INITIAL MOTION ESTIMATE IS 360/10 KT...WHICH IS BASED MAINLY ON LIMITED MICROWAVE FIXES. THE NHC MODEL GUIDANCE IS IN VERY GOOD AGREEMENT ON GABRIELLE MOVING NORTHWARD TO NORTH-NORTHWESTWARD AND SLOWING DOWN DURING THE NEXT 36 TO 48 HOURS AS THE CYCLONE MOVES AROUND THE EASTERN PERIPHERY OF A RETROGRADING MID-/UPPER-LEVEL LOW CURRENTLY LOCATED JUST NORTH OF THE BAHAMAS. ON THE FORECAST TRACK...GABRIELLE IS EXPECTED TO PASS OVER OR NEAR BERMUDA IN ABOUT 24 HOURS. BY 72 HOURS...GABRIELLE IS FORECAST TO BEGIN TO LIFT OUT AND ACCELERATE NORTHWARD AND THEN NORTHEASTWARD AHEAD OF A STRONG MID-TROPOSPHERIC TROUGH AND FRONTAL SYSTEM THAT IS FORECAST TO MOVE OFF OF THE U.S. EAST COAST BY 96 HOURS. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE MULTI-MODEL CONSENSUS TVCA. GABRIELLE IS EXPECTED TO REMAIN IN A MODERATE SHEAR ENVIRONMENT BUT OVER 28-29C SSTS FOR THE NEXT 24 HOURS OR SO...WHICH SHOULD ALLOW FOR SOME ADDITONAL STRENGTHENING TO OCCUR. THE INTENSITY IS EXPECTED TO LEVEL OFF BY 48 HOURS AS SOUTHWESTERLY VERTICAL WIND SHEAR BEGINS TO GRADUALLY INCREASE AHEAD OF THE AFOREMENTIONED APPROACHING FRONTAL SYSTEM. AT 72 HOURS AND BEYOND...GABRIELLE WILL BE MOVING OVER SUB-25C SSTS AND THE CYCLONE IS FORECAST TO BECOME A POST-TROPICAL/EXTRATROPICAL LOW BY 96 HOURS WHEN WATER TEMPERATURES WILL BE LESS THAN 20C. THE NHC INTENSITY FORECAST IS CLOSE TO THE CONSENSUS MODEL ICON. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 29.6N 65.0W 35 KT 40 MPH 12H 10/1800Z 31.1N 65.0W 40 KT 45 MPH 24H 11/0600Z 32.7N 65.2W 45 KT 50 MPH 36H 11/1800Z 33.7N 65.7W 45 KT 50 MPH 48H 12/0600Z 34.5N 66.3W 45 KT 50 MPH 72H 13/0600Z 37.7N 65.9W 45 KT 50 MPH 96H 14/0600Z 46.8N 58.6W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 15/0600Z 56.5N 41.9W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ FORECASTER STEWART WTNT42 KNHC 101439 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 AM AST TUE SEP 10 2013 THE CONVECTIVE PATTERN OF GABRIELLE CONTINUES TO FEATURE VERY COLD CLOUD TOPS IN A CDO TYPE FEATURE. MICROWAVE AND GEOSTATIONARY SATELLITE IMAGERY CONTINUE TO SUGGEST THAT THE LOW-LEVEL CENTER IS LOCATED ON THE SOUTHWESTERN SIDE OF THE DEEP CONVECTION...AND THIS STRUCTURE IS CONSISTENT WITH THE 25 KT OR SO OF SOUTHWESTERLY SHEAR ANALYZED OVER THE SYSTEM BY UW-CIMSS. THE INITIAL INTENSITY REMAINS 35 KT IN AGREEMENT WITH THE LATEST DVORAK CLASSIFICATIONS FROM TAFB AND SAB. AN AIR FORCE RESERVE AIRCRAFT WILL INVESTIGATE GABRIELLE THIS AFTERNOON TO PROVIDE MORE DETAILED INFORMATION ON THE EXACT LOCATION AND STRENGTH OF THE CYCLONE. THE ENVIRONMENT WILL REMAIN MARGINAL FOR STRENGTHENING DURING THE NEXT COUPLE OF DAYS...AS GABRIELLE REMAINS OVER SSTS ABOVE 27C WITH MODERATE SOUTHWESTERLY TO WESTERLY VERTICAL SHEAR. THE NHC INTENSITY FORECAST IS UNCHANGED FROM THE PREVIOUS ADVISORY AND IS CLOSE TO THE CONSENSUS AIDS FOR THE FIRST 48 HOURS. LATE IN THE PERIOD...THE GLOBAL MODELS SHOW LITTLE CHANGE IN INTENSITY DURING AND AFTER EXTRATROPICAL TRANSITION...WHICH SHOULD BE COMPLETE BY 96 HOURS. GABRIELLE SHOULD DISSIPATE OR BE ABSORBED BY DAY 5. THE INITIAL MOTION ESTIMATE IS 360/10...AS THE CYCLONE IS CURRENTLY SITUATED BETWEEN A MID-LEVEL RIDGE TO THE EAST AND A MID/UPPER- LEVEL LOW TO THE WEST. THE FORWARD MOTION OF GABRIELLE WILL SLOW AS THE STEERING FLOW WEAKENS...AND THE CYCLONE SHOULD TURN GRADUALLY TOWARD THE NORTHWEST BY 48 HOURS. LATER IN THE PERIOD...GABRIELLE WILL ACCELERATE NORTHEASTWARD AHEAD OF A DEEP-LAYER TROUGH MOVING INTO EASTERN NORTH AMERICA IN 3-4 DAYS. THE NHC FORECAST IS LARGELY AN UPDATE OF THE PREVIOUS ONE THROUGH 48 HOURS AND THEN TRENDS A LITTLE SLOWER AT DAYS 3 AND 4...LYING BETWEEN THE FASTER ECMWF AND THE SLOWER TVCA MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 30.6N 65.0W 35 KT 40 MPH 12H 11/0000Z 31.9N 64.9W 40 KT 45 MPH 24H 11/1200Z 33.1N 65.2W 45 KT 50 MPH 36H 12/0000Z 34.0N 65.8W 45 KT 50 MPH 48H 12/1200Z 35.2N 66.2W 45 KT 50 MPH 72H 13/1200Z 39.5N 65.0W 45 KT 50 MPH 96H 14/1200Z 49.0N 56.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 15/1200Z...DISSIPATED $$ FORECASTER BRENNAN WTNT42 KNHC 101715 TCDAT2 TROPICAL STORM GABRIELLE SPECIAL DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 130 PM AST TUE SEP 10 2013 A PAIR OF ASCAT PASSES FROM 1342Z AND 1436Z INDICATE THAT GABRIELLE IS STRONGER THAN PREVIOUSLY ESTIMATED. BOTH PASSES SHOWED SEVERAL 45-KT WIND RETRIEVALS...AND THAT IS THE INITIAL INTENSITY FOR THIS SPECIAL ADVISORY. THE INTENSITY FORECAST HAS BEEN ADJUSTED UPWARD AT 12 AND 24 HOURS TO 50 KT BASED ON THE INCREASE IN THE INITIAL INTENSITY. THE ANALYZED 34-KT WIND RADII HAVE ALSO BEEN ADJUSTED OUTWARD BASED ON THE ASCAT DATA...AND THEIR FORECAST HAS BEEN MODIFIED AS WELL TO REFLECT THE LARGER WIND FIELD. AN AIR FORCE RESERVE AIRCRAFT WILL INVESTIGATE GABRIELLE LATER THIS AFTERNOON TO PROVIDE MORE DETAILED INFORMATION ON THE STRENGTH AND STRUCTURE OF THE CYCLONE. NO CHANGES WERE MADE TO THE PREVIOUS TRACK FORECAST FOR THIS SPECIAL ADVISORY. NOTE THAT THIS SPECIAL ADVISORY TAKES THE PLACE OF THE 200 PM AST/1800 UTC INTERMEDIATE ADVISORY. FORECAST POSITIONS AND MAX WINDS INIT 10/1730Z 30.9N 64.8W 45 KT 50 MPH 12H 11/0000Z 31.9N 64.9W 50 KT 60 MPH 24H 11/1200Z 33.1N 65.2W 50 KT 60 MPH 36H 12/0000Z 34.0N 65.8W 45 KT 50 MPH 48H 12/1200Z 35.2N 66.2W 45 KT 50 MPH 72H 13/1200Z 39.5N 65.0W 45 KT 50 MPH 96H 14/1200Z 49.0N 56.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 15/1200Z...DISSIPATED $$ FORECASTER BRENNAN WTNT42 KNHC 102056 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 PM AST TUE SEP 10 2013 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING GABRIELLE FOUND PEAK SFMR WINDS OF 45-50 KT NORTHWEST AND SOUTHEAST OF THE CENTER ON THEIR FIRST PASS THROUGH THE STORM...AND THE INITIAL INTENSITY IS INCREASED TO 50 KT FOR THIS ADVISORY. THE CENTRAL PRESSURE OF 1004 MB IS BASED ON A DROPSONDE FROM THE AIRCRAFT. GABRIELLE HAS BEEN ABLE TO STRENGTHEN TODAY DESPITE THE PRESENCE OF MODERATE SOUTHWESTERLY SHEAR WHICH HAS EXPOSED THE LOW-LEVEL CENTER TO THE SOUTHWEST OF THE DEEP CONVECTION. WHILE MODERATE SHEAR IS EXPECTED TO CONTINUE OR EVEN INCREASE OVER THE NEXT COUPLE OF DAYS...THE STATISTICAL/DYNAMICAL AND GLOBAL MODELS SHOW SOME STRENGTHENING DURING THAT TIME. THIS SEEMS TO BE SUPPORTED BY MARGINAL SSTS AND AN INCREASE IN UPPER-LEVEL DIVERGENCE AHEAD OF A MID/UPPER-LEVEL TROUGH. THE NHC FORECAST SHOWS THE POTENTIAL FOR SOME STRENGTHENING AND THEN LITTLE CHANGE THROUGH EXTRATROPICAL TRANSITION IN ABOUT 96 HOURS. THE INITIAL MOTION ESTIMATE IS 360/09. THE MODEL GUIDANCE SHOWS A TURN TOWARD THE NORTH-NORTHWEST WITH A DECREASE IN FORWARD SPEED OVER THE NEXT 12 TO 24 HOURS...AS GABRIELLE IS TUGGED WESTWARD BY A WEAKENING MID/UPPER-LEVEL LOW CURRENTLY SITUATED EAST OF FLORIDA. AT 48 HOURS AND BEYOND...AN ACCELERATION TOWARD THE NORTHEAST IS EXPECTED AHEAD OF A DEEP-LAYER TROUGH MOVING THROUGH EASTERN NORTH AMERICA. THE TRACK MODELS REMAIN IN REASONABLE AGREEMENT ON THE OVERALL SCENARIO...HOWEVER MUCH OF THE GUIDANCE HAS SHIFTED A LITTLE TO THE LEFT THIS CYCLE. OVERALL...THE NHC TRACK FORECAST IS SIMILAR TO THE PREVIOUS ONE THROUGH 48 HOURS AND AFTERWARD HAS BEEN ADJUSTED A BIT TO THE LEFT...BUT STILL LIES EAST OF THE MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 31.5N 64.9W 50 KT 60 MPH 12H 11/0600Z 32.6N 65.0W 55 KT 65 MPH 24H 11/1800Z 33.5N 65.5W 55 KT 65 MPH 36H 12/0600Z 34.3N 66.0W 55 KT 65 MPH 48H 12/1800Z 35.7N 66.5W 55 KT 65 MPH 72H 13/1800Z 42.0N 63.5W 55 KT 65 MPH 96H 14/1800Z 52.0N 52.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 15/1800Z...DISSIPATED $$ FORECASTER BRENNAN WTNT42 KNHC 110254 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 PM AST TUE SEP 10 2013 SATELLITE IMAGERY SHOWS THAT THE PRIMARY AREA OF DEEP CONVECTION ASSOCIATED WITH GABRIELLE HAS BECOME DISPLACED WELL TO THE EAST OF THE LOW-LEVEL CENTER THIS EVENING...DUE TO STRONG SOUTHWESTERLY SHEAR. RADAR IMAGES FROM BERMUDA HAVE BEEN EXTREMELY HELPFUL IN TRACKING THE PROGRESS OF THE STORM THIS EVENING. THE RADAR DATA SHOW THAT GABRIELLE HAS DECELERATED AND THAT SOME SHALLOW CONVECTIVE BANDS ARE WRAPPING AROUND THE NORTHEASTERN PORTION OF THE CIRCULATION. THE INITIAL WIND SPEED REMAINS 50 KT...WHICH IS BASED ON THE EARLIER AIRCRAFT DATA AND RECENT OBSERVATIONS OF 35 TO 45 KT SUSTAINED WINDS AT WEATHER STATIONS ON BERMUDA. ANOTHER AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT WILL BE INVESTIGATING THE TROPICAL STORM OVERNIGHT. THE INITIAL MOTION ESTIMATE IS 355/7 KT. GABRIELLE SHOULD TURN NORTH-NORTHWESTWARD ON WEDNESDAY AS IT IS STEERED AROUND THE NORTHEASTERN SIDE OF A MID- TO UPPER-LEVEL LOW LOCATED EAST OF FLORIDA. IN A COUPLE OF DAYS...THE DEEP LAYER FLOW OFF THE EAST COAST OF THE UNITED STATES IS FORECAST TO TURN SOUTHWESTWARD AND STRENGTHEN AHEAD OF A MID-LATITUDE TROUGH. THIS SHOULD CAUSE GABRIELLE TO TURN NORTHEASTWARD AND BEGIN TO ACCELERATE. THE TRACK MODEL GUIDANCE IS IN GENERAL AGREEMENT ON THIS SCENARIO...BUT HAS SHIFTED A LITTLE WESTWARD DURING THE FIRST 36 HOURS. CONSEQUENTLY...THE NHC TRACK HAS BEEN NUDGED WESTWARD TO BE IN BETTER AGREEMENT WITH THE GUIDANCE. AFTER 36 HOURS...THE UPDATED NHC TRACK IS CLOSE TO THE PREVIOUS ADVISORY. GABRIELLE IS FORECAST TO REMAIN OVER WARM WATER BUT WITHIN MODERATE TO STRONG SOUTHWESTERLY SHEAR DURING THE NEXT FEW DAYS. THE SHEAR IS LIKELY TO PREVENT ANY SIGNIFICANT STRENGTHENING AND THE LATEST INTENSITY GUIDANCE NOW SHOWS LITTLE CHANGE IN STRENGTH DURING THE NEXT DAY OR SO. AS A RESULT...THE NHC INTENSITY FORECAST HAS BEEN ADJUSTED SLIGHTLY LOWER. IF ORGANIZED DEEP CONVECTION DOES NOT REDEVELOP IN ASSOCIATION WITH THE CYCLONE... GABRIELLE COULD DEGENERATE INTO A REMNANT LOW TOMORROW. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 32.0N 65.0W 50 KT 60 MPH 12H 11/1200Z 32.8N 65.3W 50 KT 60 MPH 24H 12/0000Z 33.6N 66.0W 45 KT 50 MPH 36H 12/1200Z 34.5N 66.6W 45 KT 50 MPH 48H 13/0000Z 36.3N 66.6W 45 KT 50 MPH 72H 14/0000Z 44.5N 61.5W 45 KT 50 MPH 96H 15/0000Z 54.0N 47.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 16/0000Z...DISSIPATED $$ FORECASTER BROWN WTNT42 KNHC 110851 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST WED SEP 11 2013 SATELLITE IMAGERY INDICATES THAT GABRIELLE IS COMPRISED OF A SWIRL OF LOW/MID-LEVEL CLOUDS WITH NO DEEP CONVECTION NEAR THE CENTER AT THIS TIME. THIS IS LIKELY DUE TO THE ONGOING AFFECT OF 15-20 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR. AN EARLIER ASCAT OVERPASS... RECENT REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT...AND OBSERVATIONS FROM BERMUDA SHOW THAT THE WINDS HAVE DECREASED DURING THE PAST 12 HOURS. THE INITIAL INTENSITY IS REDUCED TO 45 KT...AND THIS COULD BE GENEROUS. THE CYCLONE HAS TURNED TO THE LEFT SINCE THE PREVIOUS ADVISORY...AND THE INITIAL MOTION IS NOW 325/7. THIS IS PARTLY DUE TO AN UPPER- LEVEL LOW TO THE SOUTHWEST OF GABRIELLE AND A STRENGTHENING LOW/MID-LEVEL RIDGE TO THE NORTH. THIS COMBINATION SHOULD STEER GABRIELLE SLOWLY TOWARD THE NORTHWEST FOR THE NEXT 24 HOURS OR SO. AFTER THAT...THE CYCLONE IS LIKELY TO RECURVE ON THE EASTERN SIDE OF A LARGE DEEP-LAYER TROUGH MOVING INTO THE EASTERN UNITED STATES AND THE WESTERN ATLANTIC. WHILE THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THIS SCENARIO...IT HAS SHIFTED QUITE A BIT TO THE LEFT/WEST DURING THE FIRST 48 HOURS. THE NEW FORECAST TRACK IS ALSO SHIFTED TO THE LEFT DURING THAT TIME...BUT STILL LIES TO THE RIGHT OF THE CONSENSUS MODELS AND THE MIDDLE OF THE GUIDANCE ENVELOPE. GABRIELLE IS FORECAST TO REMAIN OVER WARM SEA SURACE TEMPERATURES FOR THE NEXT 48 HOURS. HOWEVER...THE DYNAMICAL MODELS CALL FOR CONTINUED STRONG SHEAR...WITH THE UKMET...NAVGEM...AND ECMWF MODELS FORECASTING THE CYCLONE TO DECAY TO A TROUGH DURING THIS TIME. AFTER THAT...WHATEVER IS LEFT OF THE CYCLONE IS EXPECTED TO MERGE WITH A FRONTAL SYSTEM BETWEEN 48-72 HOURS. THE INTENSITY FORECAST FOLLOWS THE GFS SCENARIO THAT GABRIELLE WILL REMAIN A TROPICAL CYCLONE UNTIL IT MERGES WITH THE FRONT...WITH THE NEW FORECAST A LITTLE WEAKER THAN THE PREVIOUS FORECAST. HOWEVER...AN ALTERNATIVE SCENARIO IS THAT THE CYCLONE DECAYS TO A REMNANT LOW OR TROUGH DURING THE NEXT 48 HOURS DUE TO A LACK OF CONVECTION. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 32.5N 65.7W 45 KT 50 MPH 12H 11/1800Z 33.1N 66.2W 45 KT 50 MPH 24H 12/0600Z 33.7N 66.8W 45 KT 50 MPH 36H 12/1800Z 34.7N 67.3W 40 KT 45 MPH 48H 13/0600Z 37.2N 66.5W 40 KT 45 MPH 72H 14/0600Z 46.5N 59.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 15/0600Z...DISSIPATED $$ FORECASTER BEVEN WTNT42 KNHC 111436 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 AM AST WED SEP 11 2013 GABRIELLE IS BARELY HANGING ON AS A TROPICAL CYCLONE...WITH A SMALL AREA OF DEEP CONVECTION TO THE EAST OF THE EXPOSED LOW-LEVEL CENTER. THIS IS LIKELY DUE TO THE 15-20 KT OF SOUTHWESTERLY SHEAR OVER THE CYCLONE. THE INTITAL INTENSITY HAS BEEN CONSERVATIVELY LOWERED TO 40 KT FOR THIS ADVISORY. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT 36 HOURS OR SO AS MODERATE SHEAR CONTINUES...BUT SOME INTENSIFICATION IS SHOWN AT 48 HOURS AS AN UPPER-LEVEL TROUGH MAY PROVIDE SOME BAROCLINIC SUPPORT FOR INTENSIFICATION. BY 72 HOURS...GABRIELLE SHOULD BE EXTRATROPICAL AND BE ABSORBED OR DISSIPATE SHORTLY THEREAFTER. ALTERNATIVELY...IF DEEP CONVECTION DISSIPATES ENTIRELY...GABRIELLE COULD BECOME A POST-TROPICAL CYCLONE AT ANY TIME DURING THE FORECAST PERIOD. THE CYCLONE HAS BEEN MOVING LITTLE OVER THE PAST FEW HOURS...AND IS NOW DRIFTING WESTWARD AT ABOUT 3 KT. HOWEVER THE MODEL GUIDANCE IS IN GOOD AGREEMENT ON A SLOW NORTHWESTWARD MOTION DEVELOPING DURING THE NEXT 12 TO 24 HOURS DUE TO AN UPPER-LEVEL LOW TO THE SOUTHWEST OF GABRIELLE AND A LOW/MID-LEVEL RIDGE TO THE NORTH AND NORTHEAST. RECURVATURE IS EXPECTED BY 48 HOURS AS THE CYCLONE ACCELERATES NORTH-NORTHEASTWARD AHEAD OF AN ADVANCING MID/UPPER-LEVEL TROUGH. THE TRACK MODEL GUIDANCE HAS TRENDED A LITTLE SLOWER AND TO THE LEFT THIS CYCLE AND SO HAS THE NHC TRACK WHICH NOW LIES ALONG...BUT IS A LITTLE FASTER THAN...THE TVCA MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 32.5N 65.9W 40 KT 45 MPH 12H 12/0000Z 33.1N 66.5W 40 KT 45 MPH 24H 12/1200Z 33.8N 67.1W 40 KT 45 MPH 36H 13/0000Z 35.5N 67.2W 40 KT 45 MPH 48H 13/1200Z 38.6N 65.9W 45 KT 50 MPH 72H 14/1200Z 48.5N 58.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 15/1200Z...DISSIPATED $$ FORECASTER BRENNAN WTNT42 KNHC 112036 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 PM AST WED SEP 11 2013 GABRIELLE CONTINUES TO MAINTAIN A SMALL AREA OF DEEP CONVECTION TO THE NORTHEAST OF THE CENTER IN AN ENVIRONMENT OF MODERATE SOUTHWESTERLY SHEAR. THE INITIAL INTENSITY IS LOWERED TO 35 KT BASED ON THE LATEST DVORAK DATA-T NUMBER FROM TAFB. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT 24 HOURS OR SO AS MODERATE SHEAR CONTINUES...BUT SOME INTENSIFICATION IS SHOWN FROM 36 TO 48 HOURS AS AN UPPER-LEVEL TROUGH MAY PROVIDE SOME BAROCLINIC SUPPORT FOR INTENSIFICATION. GABRIELLE SHOULD BECOME EXTRATROPICAL BY 72 HOURS...AND MAY BE DISSIPATED ENTIRELY BY THEN...HOWEVER A 72-HOUR POINT WAS PROVIDED IN THIS FORECAST FOR CONTINUITY. ALTERNATIVELY...IF DEEP CONVECTION DISSIPATES ENTIRELY...GABRIELLE COULD BECOME A POST-TROPICAL CYCLONE AT ANY TIME DURING THE FORECAST PERIOD. GABRIELLE HAS MOVED SLOWLY WEST-NORTHWESTWARD THIS AFTERNOON...AND THE INITIAL MOTION ESTIMATE IS 295/04. THIS MOTION IS PROBABLY DUE TO THE SHALLOW CYCLONE NOT FEELING THE INFLUENCE OF THE UPPER-LEVEL LOW OFF THE SOUTHEAST U.S. COAST AND THE DOMINANT STEERING FLOW COMING FROM A WEAK LOW-LEVEL RIDGE TO THE NORTH AND EAST. THE MODEL GUIDANCE CONTINUES TO INSIST ON A NORTHWARD TURN SOON...WITH A MOTION TOWARD THE NORTHWEST EXPECTED TOMORROW FOLLOWED BY A NORTH-NORTHEASTWARD ACCELERATION ON FRIDAY AHEAD OF AN EASTWARD-MOVING UPPER-LEVEL TROUGH. DUE TO THE WESTWARD MOTION TODAY...AND A WESTWARD SHIFT IN THE GUIDANCE DURING THE FIRST COUPLE OF DAYS...THE NHC FORECAST HAS BEEN ADJUSTED WESTWARD TOWARD THE NEW MULTI-MODEL CONSENSUS AND LIES ABOUT A DEGREE WEST OF THE PREVIOUS FORECAST BY 48 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 32.8N 66.4W 35 KT 40 MPH 12H 12/0600Z 33.2N 67.1W 35 KT 40 MPH 24H 12/1800Z 34.4N 67.7W 35 KT 40 MPH 36H 13/0600Z 37.1N 67.2W 40 KT 45 MPH 48H 13/1800Z 41.5N 65.0W 45 KT 50 MPH 72H 14/1800Z 51.5N 55.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 15/1800Z...DISSIPATED $$ FORECASTER BRENNAN WTNT42 KNHC 120247 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 PM AST WED SEP 11 2013 DEEP CONVECTION ASSOCIATED WITH GABRIELLE HAS DISSIPATED AGAIN THIS EVENING...LEAVING THE CYCLONE AS A SWIRL OF LOW-LEVEL CLOUDS...EXCEPT FOR ONE SMALL THUNDERSTORM THAT HAS RECENTLY DEVELOPED WELL EAST OF THE CENTER. SUBJECTIVE AND OBJECTIVE DVORAK INTENSITY ESTIMATES HAVE DECREASED BELOW TROPICAL STORM STRENGTH... AND BASED ON THESE DATA THE SYSTEM HAS BEEN DOWNGRADED TO A 30-KT TROPICAL DEPRESSION. LITTLE CHANGE IN STRENGTH IS EXPECTED DURING THE NEXT 24 HOURS AS THE CYCLONE REMAINS WITHIN AN AREA OF MODERATE WESTERLY WIND SHEAR AND DRY MID-LEVEL AIR. SOME INTENSIFICATION IS POSSIBLE AS GABRIELLE INTERACTS WITH A MID- TO UPPER-LEVEL TROUGH IN 36 TO 48 HOURS. THE TROUGH IS EXPECTED TO PROVIDE SOME BAROCLINIC FORCING AND SHOULD ALSO CAUSE THE CYCLONE TO BECOME EXTRATROPICAL IN ABOUT 2 DAYS. THE SYSTEM IS LIKELY TO BE ABSORBED BY A FRONT OVER NOVA SCOTIA SHORTLY THEREAFTER...HOWEVER A 72-HOUR POINT WAS PROVIDED ONCE AGAIN FOR FORECAST CONTINUITY. WITH THE LACK OF DEEP CONVECTION THIS EVENING...AN ALTERNATIVE SCENARIO IS THAT GABRIELLE COULD DEGENERATE INTO A REMNANT LOW ON THURSDAY OR BECOME AN OPEN TROUGH AS IT BEGINS TO ACCELERATE NORTH- NORTHEASTWARD IN A DAY OR SO. GABRIELLE CONTINUES MOVING SLOWLY WEST-NORTHWESTWARD. THE CYCLONE SHOULD TURN NORTHWARD ON THURSDAY AS IT IS STEERED AROUND THE WESTERN PORTION OF A LOW- TO MID-LEVEL RIDGE OVER THE WEST-CENTRAL ATLANTIC. AFTER 24 HOURS...GABRIELLE IS FORECAST TO ACCELERATE NORTH-NORTHEASTWARD AHEAD OF THE TROUGH MOVING INTO THE NORTHEASTERN UNITED STATES. THE TRACK GUIDANCE AGREES ON THIS SCENARIO AND THE UPDATED NHC TRACK IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 33.0N 67.0W 30 KT 35 MPH 12H 12/1200Z 33.7N 67.6W 30 KT 35 MPH 24H 13/0000Z 35.7N 67.6W 30 KT 35 MPH 36H 13/1200Z 39.4N 66.1W 35 KT 40 MPH 48H 14/0000Z 44.4N 62.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 15/0000Z 54.5N 50.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 16/0000Z...ABSORBED BY FRONT $$ FORECASTER BROWN WTNT42 KNHC 120847 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST THU SEP 12 2013 A NEW BURST OF CONVECTION HAS FORMED JUST EAST OF THE CENTER OF GABRIELLE DURING THE PAST FEW HOURS. THE SATELLITE INTENSITY ESTIMATE FROM TAFB IS 30 KT...AND AN EARLIER OSCAT OVERPASS SHOWED 25-30 KT WINDS NORTHEAST OF THE CENTER. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 30 KT. ALTHOUGH GABRIELLE REMAINS SHEARED...ANALYSES FROM CIMSS INDICATE THAT THE SHEAR HAS DECREASED TO 10-15 KT OVER THE PAST 24 HOURS. THE INITIAL MOTION IS NOW 305/6. WATER VAPOR IMAGERY AND SURFACE OBSERVATIONS SHOW A DEEP-LAYER TROUGH AND ASSOCIATED SURFACE COLD FRONT MOVING INTO THE NEW ENGLAND STATES. THE DYNAMICAL MODELS FORECAST A LOW TO FORM ON THE FRONT DURING THE NEXT 48 HOURS. THIS EVOLUTION SHOULD CREATE A BREAK IN THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC AND ALLOW GABRIELLE TO RECURVE INTO THE WESTERLIES. THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK...CALLING FOR A TURN TOWARD THE NORTH DURING THE NEXT 24 HOURS FOLLOWED BY A NORTH-NORTHEASTWARD ACCELERATION TOWARD ATLANTIC CANADA. THE TRACK GUIDANCE CONTINUES TO AGREE ON THIS SCENARIO...AND THE NEW TRACK IS AGAIN AN UPDATE OF THE PREVIOUS ADVISORY. THE INTENSITY FORECAST IS A LITTLE TRICKY. ON ONE SIDE...THE DECREASED SHEAR...24 HOURS BEFORE CROSSING THE NORTH WALL OF THE GULF STREAM...AND POSSIBLE INTERACTION WITH A BAROCLINIC TROUGH SUGGEST SOME POTENTIAL FOR STRENGTHENING. ON THE OTHER HAND...THE CYCLONE IS LIKELY TO MERGE WITH THE NON-TROPICAL SYSTEM IN 36-48 HOURS...AND THE DYNAMICAL MODELS ARE IN GOOD AGREEMENT IN THE CYCLONE DECAYING TO A TROUGH IN 36 HOURS OR LESS. ON THE PREMISE THAT THE PROS WILL OUTWEIGH THE CONS...THE INTENSITY FORECAST SHOWS MODEST STRENGTHENING BEFORE EXTRATROPICAL TRANSITION. THE ALTERNATIVE SCENARIO REMAINS THAT GABRIELLE COULD DECAY TO A REMNANT LOW OR TROUGH AT ANY TIME DURING THE NEXT 48 HOURS. AFTER EXTRATROPICAL TRANSITION...THE CYCLONE OR ITS REMNANTS WILL QUICKLY BE ABSORBED BY THE LARGER NON-TROPICAL LOW. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 33.5N 67.7W 30 KT 35 MPH 12H 12/1800Z 34.4N 67.9W 30 KT 35 MPH 24H 13/0600Z 36.9N 67.5W 35 KT 40 MPH 36H 13/1800Z 41.2N 65.4W 35 KT 40 MPH 48H 14/0600Z 46.7N 61.8W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 15/0600Z...DISSIPATED $$ FORECASTER BEVEN WTNT42 KNHC 121432 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 AM AST THU SEP 12 2013 DURING THE PAST SEVERAL HOURS...DEEP CONVECTION HAS RE-DEVELOPED NEAR THE CENTER OF GABRIELLE. GIVEN THE DISTANCE BETWEEN THE CENTER AND THE CONVECTION...AND THE PRESENCE OF A CURVED CONVECTIVE BAND TO THE EAST...IT IS ESTIMATED THAT THE WINDS ARE UP TO 35 KNOTS. THE TROPICAL STORM IS EMBEDDED WITHIN A SHEARED ENVIRONMENT...AND CONVECTION COULD EASILY BE REMOVED AGAIN. ON THAT BASIS...GABRIELLE COULD EXPERIENCE SMALL FLUCTUATIONS IN INTENSITY DURING THE NEXT 24 HOURS OR SO BEFORE IT BECOMES EXTRATROPICAL. THE CYCLONE SHOULD THEN BECOME ABSORBED BY A LARGE MID-LATITUDE TROUGH AS IT MOVES NEAR ATLANTIC CANADA. GABRIELLE IS MOVING TOWARD THE NORTH OR 350 DEGREES AT 8 KNOTS AHEAD OF A DEVELOPING MID-LATITUDE TROUGH OVER THE EASTERN UNITED STATES. THIS PATTERN WILL FORCE GABRIELLE TO RECURVE AND TURN TO THE NORTH-NORTHEAST WITH AN INCREASE IN FORWARD SPEED. THE NHC FORECAST IS IN THE MIDDLE OF THE LATEST GUIDANCE ENVELOPE. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 33.9N 67.7W 35 KT 40 MPH 12H 13/0000Z 35.0N 67.9W 35 KT 40 MPH 24H 13/1200Z 38.0N 67.0W 35 KT 40 MPH 36H 14/0000Z 43.0N 64.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 14/1200Z...DISSIPATED $$ FORECASTER AVILA WTNT42 KNHC 130252 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 PM AST THU SEP 12 2013 ONCE AGAIN DEEP CONVECTION HAS LARGELY DISAPPEARED NEAR THE CENTER OF GABRIELLE. THE INITIAL INTENSITY REMAINS 35 KT...BUT THIS COULD BE GENEROUS. WEAKENING IS FORECAST AS THE CYCLONE ACCELERATES NORTHEASTWARD AND IS ABSORBED BY A FRONTAL SYSTEM IN 36 HOURS OR PERHAPS A LITTLE SOONER. GABRIELLE IS NOW MOVING TOWARD THE NORTH-NORTHEAST OR 015 DEGREES AT ABOUT 9 KNOTS AHEAD OF A DEVELOPING MID-LATITUDE TROUGH OVER THE EASTERN UNITED STATES. GABRIELLE SHOULD CONTINUE TO ACCELERATE NORTH-NORTHEASTWARD ON FRIDAY...AND THE NHC TRACK IS IN GOOD AGREEMENT WITH THE MODEL GUIDANCE THROUGH DISSIPATION. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 35.1N 67.7W 35 KT 40 MPH 12H 13/1200Z 38.0N 66.8W 30 KT 35 MPH 24H 14/0000Z 43.8N 64.3W 30 KT 35 MPH...POST-TROP/EXTRATROP 36H 14/1200Z...DISSIPATED $$ FORECASTER BRENNAN WTNT42 KNHC 130851 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST FRI SEP 13 2013 ALTHOUGH DEEP CONVECTION HAS INCREASED TO THE NORTH OF THE CENTER OF GABRIELLE DURING THE LAST FEW HOURS...IT LACKS BANDING FEATURES. AN ASCAT OVERPASS AROUND 0200 UTC SHOWED MAXIMUM WINDS IN THE 25 TO 30 KT RANGE...AND ALL OF THE SATELLITE INTENSITY ESTIMATES SUPPORT AN INTENSITY OF 30 KT OR LOWER. BASED ON THESE DATA...GABRIELLE IS ONCE AGAIN DOWNGRADED TO A 30-KT TROPICAL DEPRESSION. GABRIELLE IS MOVING A LITTLE FASTER THAN IT WAS EARLIER...WITH THE LATEST INITIAL MOTION ESTIMATE BEING 015/15. THE CYCLONE IS EXPECTED TO ACCELERATE TO THE NORTH-NORTHEAST LATER TODAY WHEN IT BECOMES MORE EMBEDDED IN THE STRONG FLOW ON THE EAST SIDE OF A DEEP-LAYER TROUGH OVER THE EASTERN UNITED STATES AND CANADA. GABRIELLE IS FORECAST TO DEGENERATE INTO A TROUGH IN 12 TO 24 HOURS BEFORE IT IS ABSORBED BY A COLD FRONT. SOME OF THE DYNAMICAL MODELS SHOW DISSIPATION OCCURRING EVEN SOONER THAN FORECAST. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 36.5N 67.5W 30 KT 35 MPH 12H 13/1800Z 40.5N 65.8W 30 KT 35 MPH 24H 14/0600Z...DISSIPATED $$ FORECASTER CANGIALOSI WTNT42 KNHC 131440 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 AM AST FRI SEP 13 2013 AMBIGUITIES FROM AN 0200 UTC ASCAT PASS SUGGEST THAT THERE ARE VERY LITTLE...IF ANY...NORTHERLY WINDS ON THE WEST SIDE OF THE CIRCULATION. GABRIELLE HAS ACCELERATED TOWARD THE NORTH-NORTHEAST SINCE THAT TIME...REDUCING THE LIKELIHOOD THAT NORTH WINDS ARE PRESENT. HOWEVER...A LARGE BURST OF CONVECTION DURING THE PAST 6 HOURS AT LEAST MAKES IT PLAUSIBLE THAT THE CIRCULATION REMAINS CLOSED...AND SO GABRIELLE IS BEING HELD AS A 30 KT TROPICAL DEPRESSION FOR THIS ADVISORY. A SLIGHT INCREASE IN THE MAXIMUM WINDS IS POSSIBLE TODAY DUE TO BAROCLINIC PROCESSES. THE FORWARD SPEED OF GABRIELLE HAS INCREASED DURING THE PAST FEW HOURS...AND THE INITIAL MOTION ESTIMATE IS NOW 020/20. ALL OF THE DYNAMICAL MODELS SUGGEST THAT THE DEPRESSION WILL CONTINUE TO ACCELERATE TOWARD THE NORTH-NORTHEAST WHILE IT INTERACTS WITH A DEEP-LAYER TROUGH LOCATED OVER THE EASTERN UNITED STATES AND CANADA. THE GUIDANCE SUGGESTS THAT GABRIELLE WILL OPEN UP INTO A TROUGH LATER TODAY...ALTHOUGH THE OFFICIAL FORECAST CONSERVATIVELY SHOWS A 12-HOUR FORECAST POINT. AFTER THAT...GABRIELLE OR ITS REMNANTS SHOULD GET ABSORBED BY AN APPROACHING COLD FRONT. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 39.1N 66.5W 30 KT 35 MPH 12H 14/0000Z 43.2N 64.6W 35 KT 40 MPH...POST-TROPICAL 24H 14/1200Z...DISSIPATED $$ FORECASTER FRANKLIN/ZELINSKY