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Tropical Storm Sebastien Forecast Discussion Number 17
2019-11-23 15:54:09| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sat Nov 23 2019 000 WTNT45 KNHC 231454 TCDAT5 Tropical Storm Sebastien Discussion Number 17 NWS National Hurricane Center Miami FL AL202019 1100 AM AST Sat Nov 23 2019 First-light visible imagery and a few late-arriving microwave overpasses revealed that Sebastien's elongated center is located well northeast of previous estimates. It isn't clear if the center reformed or if it simply accelerated more than expected overnight, but the initial motion estimate is now 055/23 kt. A significant change to the track forecast was made based on the updated initial position, and the NHC forecast now shows a much faster motion for Sebastien. The cyclone's cloud pattern is somewhat ragged and does not look entirely tropical. That said, Sebastien is still producing enough deep convection to be classified as a tropical storm. Unfortunately, no ASCAT data was available this morning to help assess the strength of the winds or how well-defined the circulation is at the surface. The initial intensity is conservatively maintained at 55 kt based primarily on continuity from previous advisories, but this could be generous since Dvorak intensity estimates are lower. Every aspect of the forecast remains highly uncertain. The models have been extremely inconsistent in forecasting Sebastien, with the guidance varying drastically from run to run and with unusually large spread in each forecast. The latest indications are that Sebastien will move quickly northeastward with little change in strength for the next few days before it eventually opens into a trough around the time it nears the Azores in a couple of days. Simulated satellite imagery suggests that the cyclone will still produce enough deep convection to be classified as a tropical storm through Sunday, though it could become post-tropical before it reaches the Azores. Given the elongated nature of Sebastien's circulation and its fast forward speed, it could also open into a trough and dissipate at any time. It is not currently clear if Sebastien will reach the Azores as a tropical storm. Regardless of its status, Sebastien or its remnants could bring gusty winds and rain to the Azores beginning Sunday. Please see products issued by the Portuguese Institute for the Sea and the Atmosphere (IPMA) for more information. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 30.4N 47.7W 55 KT 65 MPH 12H 24/0000Z 32.1N 44.5W 55 KT 65 MPH 24H 24/1200Z 34.4N 40.0W 55 KT 65 MPH 36H 25/0000Z 36.8N 34.0W 55 KT 65 MPH 48H 25/1200Z 39.3N 26.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 26/1200Z...DISSIPATED $$ Forecaster Zelinsky
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