1WTNT41 KNHC 220249 2TCDAT1 3 4Tropical Depression Eleven Discussion Number 1 5NWS National Hurricane Center Miami FL AL112018 61100 PM AST Fri Sep 21 2018 7 8The small, but well-defined, low pressure system located about 500 9miles east of the Lesser Antilles has been producing steady 10convection for the past several hours. Although this convection is 11displaced to the south and east of the exposed low-level center due 12to strong westerly wind shear, it has persisted long enough to meet 13the NHC definition of a tropical cyclone. On this basis, advisories 14are being initiated on Tropical Depression Eleven. 15 16The initial intensity is set at 30 kt based on ASCAT data from 17earlier today which showed a couple of 25-30 kt wind vectors in the 18northeast quadrant of the circulation. The intensity guidance is in 19extremely good agreement that the depression is unlikely to 20strengthen. All of the global models forecast an increase in 21upper-level winds over the small cyclone during the next 24 h. In 22fact, SHIPS diagnostics indicate that the 850-200 mb shear could 23exceed 30 kt by tomorrow morning, and will be near 40 kt within 48 24h. As a result of this shear and some dry air also in the vicinity, 25the dynamical models unanimously forecast dissipation within 72 h, 26and most show that the depression will open into a trough of low 27pressure sooner than that. The NHC forecast conservatively maintains 28the tropical cyclone for 48 h, but it could weaken and dissipate 29sooner than currently indicated. 30 31The depression has recently been moving almost due west, but a 32longer-term motion yields an initial motion of 290/5 kt. A break in 33the subtropical ridge to the north of the depression should result 34in fairly weak steering flow for the next day or two, and only a 35slow west-northwestward to westward motion is anticipated. All of 36the typically-reliable track models are in fairly good agreement on 37this scenario. The NHC forecast is very close to HCCA at all 38forecast hours, and lies near the south edge of the tight guidance 39envelope. 40 41 42FORECAST POSITIONS AND MAX WINDS 43 44INIT 22/0300Z 13.1N 53.4W 30 KT 35 MPH 45 12H 22/1200Z 13.5N 54.2W 30 KT 35 MPH 46 24H 23/0000Z 13.8N 55.0W 30 KT 35 MPH 47 36H 23/1200Z 14.2N 56.3W 30 KT 35 MPH 48 48H 24/0000Z 14.5N 58.0W 25 KT 30 MPH 49 72H 25/0000Z...DISSIPATED 50 51$$ 52Forecaster Zelinsky 53 54 55 56------------=_1537584569-1955-1433 57Content-Type: text/plain; charset="US-ASCII" 58Content-Disposition: inline 59Content-Transfer-Encoding: 7BIT 60 61= = = == = = 62WTNT41 KNHC 220836 63TCDAT1 64 65Tropical Depression Eleven Discussion Number 2 66NWS National Hurricane Center Miami FL AL112018 67500 AM AST Sat Sep 22 2018 68 69Deep convection remains displaced to the east of the depression's 70center due to 30-40 kt of westerly shear. Although Dvorak final-T 71numbers from TAFB and SAB have decreased since yesterday--now a 72consensus T1.0--the initial intensity is held, perhaps generously, 73at 30 kt. Strong westerly shear is expected to persist for several 74days, which at the very least will prevent the depression from 75getting any better organized. Since the global models show the 76depression opening up into a trough in about 24 hours, the new NHC 77intensity forecast brings down the winds a little faster, shows the 78system becoming a remnant low by 36 hours, and dissipates the low 79entirely by 48 hours well east of the Windward Islands. This 80evolution could certainly occur more quickly than indicated by the 81official forecast. 82 83The center of the depression has not been moving much, and it's 84possible the sheared convection is trying to pull it back toward 85the east. However, the average motion over the past 12 hours is 86westward, or 270/4 kt. The track guidance insists that the 87depression should move slowly west-northwestward over the next 88couple of days, but given that the system has not made any 89northward progress, I elected to skirt the southern edge of the 90guidance envelope. This new forecast is a little south of the 91previous NHC track prediction. 92 93 94FORECAST POSITIONS AND MAX WINDS 95 96INIT 22/0900Z 13.0N 53.5W 30 KT 35 MPH 97 12H 22/1800Z 13.3N 54.3W 30 KT 35 MPH 98 24H 23/0600Z 13.6N 55.4W 25 KT 30 MPH 99 36H 23/1800Z 13.8N 56.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 100 48H 24/0600Z...DISSIPATED 101 102$$ 103Forecaster Berg 104 105 106 107------------=_1537605384-1955-1513 108Content-Type: text/plain; charset="US-ASCII" 109Content-Disposition: inline 110Content-Transfer-Encoding: 7BIT 111 112= = = == = = 113WTNT41 KNHC 221432 114TCDAT1 115 116Tropical Depression Eleven Discussion Number 3 117NWS National Hurricane Center Miami FL AL112018 1181100 AM AST Sat Sep 22 2018 119 120It appears that the depression's best day is behind it, as the 121cloud pattern has become less organized this morning. The low-level 122center is becoming increasingly separated from the warming cloud 123tops in what remains of the deep convection, which is displaced to 124the east by nearly 40 kt of west-southwesterly shear as analyzed by 125UW-CIMSS. The initial intensity has been lowered to 25 kt, 126consistent with a T1.0 classification from TAFB. Given that the 127strong shear is expected to continue and the depression will be 128moving through a relatively dry environment, the cyclone should 129gradually spin down and become a remnant low by 24 hours and 130dissipate by 48 hours. However, I would not be surprised if either 131or both of these occurred sooner. 132 133The center of the depression hasn't moved much during the past few 134hours, but a long-term initial motion estimate is 280/03. The 135weakening cyclone should be steered westward to west-northwestward 136by a low-level ridge. The new NHC track forecast is north of the 137previous one but remains along the southern edge of the guidance 138envelope given doubts about how much latitude such a shallow system 139will gain prior to dissipation. 140 141FORECAST POSITIONS AND MAX WINDS 142 143INIT 22/1500Z 13.2N 53.8W 25 KT 30 MPH 144 12H 23/0000Z 13.6N 54.5W 25 KT 30 MPH 145 24H 23/1200Z 14.0N 55.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 146 36H 24/0000Z 14.4N 56.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 147 48H 24/1200Z...DISSIPATED 148 149$$ 150Forecaster Brennan 151 152 153 154------------=_1537626749-1955-1571 155Content-Type: text/plain; charset="US-ASCII" 156Content-Disposition: inline 157Content-Transfer-Encoding: 7BIT 158 159= = = == = = 160WTNT41 KNHC 222037 161TCDAT1 162 163Tropical Depression Eleven Discussion Number 4 164NWS National Hurricane Center Miami FL AL112018 165500 PM AST Sat Sep 22 2018 166 167Since the last advisory was issued, deep convection decreased in 168association with the depression to the point that it was not 169classifiable with the Dvorak technique at 18Z. However, there are a 170couple of patches of thunderstorms that have developed recently, 171and if they persist they could help the system hold on to tropical 172cyclone status a bit longer. The low-level center remains exposed 173with UW-CIMSS now analyzing nearly 45 kt of westerly shear over the 174cyclone. Gradual spin down is expected during the next 12 to 24 175hours, and the cyclone should become a remnant low by Sunday. Global 176model fields show the surface circulation dissipating by 36 hours 177and that is indicated in the official forecast. 178 179The low-level center has been moving erratically today, with a 180recent northward jog seen, but the long-term initial motion estimate 181is 305/03. The weakening cyclone should be steered west- 182northwestward by a weak low-level ridge through dissipation, and 183the NHC track forecast has been nudged northward toward the latest 184multi-model consensus. 185 186 187FORECAST POSITIONS AND MAX WINDS 188 189INIT 22/2100Z 13.6N 53.9W 25 KT 30 MPH 190 12H 23/0600Z 13.9N 54.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 191 24H 23/1800Z 14.4N 56.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 192 36H 24/0600Z...DISSIPATED 193 194$$ 195Forecaster Brennan 196 197 198 199------------=_1537648650-1955-1649 200Content-Type: text/plain; charset="US-ASCII" 201Content-Disposition: inline 202Content-Transfer-Encoding: 7BIT 203 204= = = == = = 205WTNT41 KNHC 230235 206TCDAT1 207 208Tropical Depression Eleven Discussion Number 5 209NWS National Hurricane Center Miami FL AL112018 2101100 PM AST Sat Sep 22 2018 211 212Although deep convection has increased since earlier today, it has 213become increasingly difficult to identify a well-defined center 214associated with the depression. After moving erratically during the 215afternoon, the center of the depression appears to have become 216disrupted by convection to its east, and it is unclear at this point 217if a closed surface circulation still exists. Since visible imagery 218is not currently available and recent ASCAT data from around 0000Z 219was inconclusive, at least one more advisory will be issued under 220the assumption that the depression has not quite yet dissipated. 221 222The initial motion is highly uncertain, but it is assumed that the 223system is still moving generally northwestward, or 310/3 kt. No 224substantial changes were made to the NHC intensity or track 225forecasts. All available guidance indicates that the depression will 226continue to move slowly west-northwestward or northwestward for the 227next day or two while it gradually weakens due to continued strong 228wind shear. Given the recent increase in convection, it no longer 229seems likely that the system will become a remnant low prior to 230dissipating. Therefore, the NHC forecast now keeps the system as a 231tropical depression until dissipation occurs in 36 h, if not sooner. 232 233FORECAST POSITIONS AND MAX WINDS 234 235INIT 23/0300Z 13.8N 54.5W 25 KT 30 MPH 236 12H 23/1200Z 14.2N 55.3W 25 KT 30 MPH 237 24H 24/0000Z 14.5N 56.6W 20 KT 25 MPH 238 36H 24/1200Z...DISSIPATED 239 240$$ 241Forecaster Zelinsky 242 243 244 245------------=_1537670135-1955-1735 246Content-Type: text/plain; charset="US-ASCII" 247Content-Disposition: inline 248Content-Transfer-Encoding: 7BIT 249 250= = = == = = 251WTNT41 KNHC 230832 252TCDAT1 253 254Tropical Depression Eleven Discussion Number 6 255NWS National Hurricane Center Miami FL AL112018 256500 AM AST Sun Sep 23 2018 257 258Satellite images indicate that the depression is poorly organized. 259The circulation is becoming increasingly elongated, and it seems 260likely that a closed circulation may no longer exist. However, we 261are maintaining advisories for now to wait for visible imagery to 262better assess the low-level circulation. The depression continues 263to produce a few patches of deep convection, but these are confined 264to the east and northeast portions of the circulation due to about 26535 kt of westerly shear. The initial intensity remains 25 kt based 266on the earlier ASCAT data. 267 268The system is moving into an environment of even stronger westerly 269wind shear. These hostile winds and dry air should cause the 270depression to dissipate, if it has not already, later today or 271tonight. The depression, or its remnants, are expected to move 272slowly west-northwestward for another day or so. 273 274FORECAST POSITIONS AND MAX WINDS 275 276INIT 23/0900Z 14.5N 55.0W 25 KT 30 MPH 277 12H 23/1800Z 15.0N 56.0W 25 KT 30 MPH 278 24H 24/0600Z...DISSIPATED 279 280$$ 281Forecaster Cangialosi 282 283 284 285------------=_1537691559-1955-1823 286Content-Type: text/plain; charset="US-ASCII" 287Content-Disposition: inline 288Content-Transfer-Encoding: 7BIT 289 290= = = == = = 291