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Tropical Storm Sebastien Forecast Discussion Number 14
2019-11-22 21:32:58| National Hurricane Center (Atlantic)
Issued at 500 PM AST Fri Nov 22 2019 000 WTNT45 KNHC 222032 TCDAT5 Tropical Storm Sebastien Discussion Number 14 NWS National Hurricane Center Miami FL AL202019 500 PM AST Fri Nov 22 2019 Sebastien's structure has not changed since this morning. ASCAT data that arrived just after the issuance of the previous advisory showed that the system was producing winds slightly above 45 kt, a little higher than the previous estimate. Since the structure of the tropical storm has not changed since the time of the ASCAT, the intensity has been set at 50 kt. It should be noted that this is merely an adjustment of the intensity assessment and is not an indication of strengthening. The agreement between the intensity models is remarkably poor. In just the first 24 h of the forecast, the solutions range from dissipation (HMON), to hurricane-strength (HWRF), to steady-state (most of the global models). Since the shear is high and SSTs ahead of the cyclone will be fairly cold, the solution that makes the most sense to me is that of the global and statistical-dynamical models, which generally show slow weakening during the next couple of days. Dissipation is still expected within 72 h. The Jekyll and Hyde behavior of the models isn't limited to the intensity forecast. While it seems clear that Sebastien will move east-northeastward or northeastward along the southern end of a frontal boundary during the next couple of days, the speed at which it will move is very unclear. The deeper the cyclone remains, the more influence strong upper-level southwesterly winds will have on its track, and the faster it will likely move. The latest track guidance unanimously shows a dramatically faster forward motion of Sebastien. In fact, the consensus now shows a forward speed nearly twice as fast as the previous NHC advisory. The official forecast continues to chase the models but has not been moved nearly as far as HCCA or TVCN. Confidence in the track forecast is quite low. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 26.2N 53.7W 50 KT 60 MPH 12H 23/0600Z 27.3N 51.8W 50 KT 60 MPH 24H 23/1800Z 28.9N 49.2W 45 KT 50 MPH 36H 24/0600Z 31.0N 45.8W 45 KT 50 MPH 48H 24/1800Z 33.1N 41.5W 40 KT 45 MPH 72H 25/1800Z...DISSIPATED $$ Forecaster Zelinsky
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