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| #990291 (Received by flhurricane at: 3:39 AM 23.Nov.2019) TCDAT5 Tropical Storm Sebastien Discussion Number 16 NWS National Hurricane Center Miami FL AL202019 500 AM AST Sat Nov 23 2019 The cloud pattern of Sebastien has changed significantly overnight. Deep convection has decreased substantially during the past several hours and the remaining thunderstorms are organized around a mid-level eye feature seen in satellite images. Model vertical cross sections indicate that Sebastien is extremely titled with the low-level center, although I can`t see it, likely well displaced to the southwest of the mid-level eye. The initial intensity is held at 55 kt based on the ASCAT data that came in a little after 00 Z, but it looks like Sebastien is on a weakening trend. Strong southwesterly vertically wind shear of about 40 kt is responsible for the titled structure of the cyclone. Since the shear is not expected to let up and because Sebastien is headed for steadily cooler waters, it seems reasonable to assume that weakening is likely. Although the models agree that Sebastien should slowly lose its strength, it remains unclear if Sebastien will transition to a post-tropical cyclone before it opens up into a trough during the next few days. The NHC forecast continues to show dissipation by day 3, but it is certainty possible that it dissipates before then. The tropical storm is moving east-northeastward at 15 kt ahead of a cold front and trough. This motion with an increase in forward speed is expected during the next few days as Sebastien becomes more embedded in the faster mid-latitude flow. The models are in relatively good agreement, and only small changes were made to the previous NHC forecast. The initial wind radii were modified based on the aforementioned ASCAT passes, and the 12-ft sea radii were adjusted based on ship and altimeter data. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 27.8N 50.6W 55 KT 65 MPH 12H 23/1800Z 29.4N 48.2W 50 KT 60 MPH 24H 24/0600Z 31.6N 44.2W 45 KT 50 MPH 36H 24/1800Z 34.0N 38.8W 40 KT 45 MPH 48H 25/0600Z 37.0N 31.6W 35 KT 40 MPH 72H 26/0600Z...DISSIPATED $$ Forecaster Cangialosi |
