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Tropical Depression Fifteen Forecast Discussion Number 1
2019-10-14 22:40:30| National Hurricane Center (Atlantic)
Issued at 500 PM AST Mon Oct 14 2019 000 WTNT45 KNHC 142040 TCDAT5 Tropical Depression Fifteen Discussion Number 1 NWS National Hurricane Center Miami FL AL152019 500 PM AST Mon Oct 14 2019 The large low pressure system that moved off the coast of Africa yesterday has gradually become better defined based on earlier ASCAT scatterometer wind data and recent visible satellite imagery. Several fragmented curved bands have been developing during the past several hours, especially in the northern semicircle, and the aforementioned ASCAT passes indicated that winds of 30-32 kt were present northwest of the center. The initial intensity is set at 30 kt based on a blend of the scatterometer wind data and a satellite intensity estimate of T1.5/25 kt from SAB, and the rather broad nature of the depression. A surge of mid-level dry air has recently penetrated into the inner-core region, causing some erosion of the central deep convection. However, this is expected to be a temporary condition with convection returning later tonight and early Tuesday during the normal nocturnal convective maximum period. However, the large size of the cyclone -- more than 1000 nmi wide -- should prevent any rapid or significant intensification. With very low vertical shear conditions forecast by the GFS and ECMWF models to continue for the next 24 to 36 hours, at least some modest strengthening seems likely given the unusually warm SSTs of near 28.5 deg C that the cyclone will be traversing during that time. By 48 hours, the shear is forecast to increase from the southwest in excess of 25 kt, resulting in weakening into a remnant low shortly thereafter. By 72 hours and beyond, the shear is expected to increase to more than 40 kt, which will cause rapid weakening and dissipation by the 120-h period, if not sooner. The official intensity forecast is similar to a blend of the NOAA-HCCA and IVCN consensus models, and the GFS- and ECMWF-based Decay-SHIPS statistical intensity models. The initial motion estimate is northwestward or 310/07 kt. The latest NHC model guidance is in very good agreement on the tropical cyclone moving generally northwestward around the southwestern periphery of a deep-layer ridge for the next 48 hours. Thereafter, the models diverge significantly based on how soon the cyclone weakens and turns westward within the low-level easterly trade wind flow. The ECMWF holds on to a vertically deeper system a little longer than the GFS, UKMET, HWRF, and HMON models, resulting in a longer northwestward track. However, since the cyclone will likely have become a vertically shallow remnant low by 72 hours, the NHC official forecast track is a little to the left of ECMWF solution, closer to the TVCN and HCCA consensus model tracks at 72 and 96 h. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 13.2N 20.2W 30 KT 35 MPH 12H 15/0600Z 14.3N 21.1W 35 KT 40 MPH 24H 15/1800Z 15.5N 22.4W 40 KT 45 MPH 36H 16/0600Z 16.7N 23.4W 40 KT 45 MPH 48H 16/1800Z 18.1N 24.6W 35 KT 40 MPH 72H 17/1800Z 20.4N 26.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 18/1800Z 21.4N 29.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 19/1800Z...DISSIPATED $$ Forecaster Stewart
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