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Tropical Storm Sebastien Forecast Discussion Number 5
2019-11-20 15:47:17| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Nov 20 2019 000 WTNT45 KNHC 201447 TCDAT5 Tropical Storm Sebastien Discussion Number 5 NWS National Hurricane Center Miami FL AL202019 1100 AM AST Wed Nov 20 2019 Sebastien continues to struggle with dry air and northwesterly shear, with satellite imagery showing an exposed low-level center to the west of the deep convection. The current structure of the storm should prevent significant intensification during the next 12 hours. After that time, Sebastien will begin to interact with a mid- to upper-level trough that will produce upper-level divergence over the cyclone. This will provide a window for Sebastien to intensify before making the transition to an extratropical cyclone in about 48 hours. All available guidance intensifies the storm, and the dynamical models continue to strengthen it more than the statistical models. In fact, the mesoscale models unanimously make Sebastian a hurricane within 36 hours. However, these models are likely intensifying the cyclone too quickly over the next 12 hours, and therefore may have a slight high bias. The official forecast takes this into account and keeps the storm just below hurricane strength before extratropical transition by 48 hours, which is a blend of the ECMWF and GFS solutions. Sebastien appears to be approaching its westernmost point and a turn to the north should begin later today, followed by acceleration to the northeast starting tonight due to the influence of the approaching trough. The track guidance is in agreement on this overall scenario. The NHC forecast track is just slightly slower than the previous one in the first 24 hours, and is close to the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 21.1N 61.7W 45 KT 50 MPH 12H 21/0000Z 22.0N 61.7W 45 KT 50 MPH 24H 21/1200Z 23.7N 60.2W 55 KT 65 MPH 36H 22/0000Z 26.3N 57.2W 60 KT 70 MPH 48H 22/1200Z 29.8N 52.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 23/1200Z...DISSIPATED $$ Forecaster Latto/Mello
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