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Tropical Storm Sebastien Forecast Discussion Number 13
2019-11-22 15:49:52| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Fri Nov 22 2019 000 WTNT45 KNHC 221449 TCDAT5 Tropical Storm Sebastien Discussion Number 13 NWS National Hurricane Center Miami FL AL202019 1100 AM AST Fri Nov 22 2019 Sebastien is strongly sheared with deep convection limited to the northeast quadrant of the cyclone. The intensity has been set at 45 kt, based primarily on the latest TAFB Dvorak classification and recent ADT fixes. A partial ASCAT overpass at 1239 UTC may not have captured the strongest winds, but showed a peak value of only 40 kt. Recent visible imagery and the ASCAT data also indicate that Sebastien's circulation is not quite as well defined as it was yesterday, perhaps due to its close proximity to a nearby frontal boundary. A significant change was made to the intensity forecast earlier this morning, and the latest forecast is in line with that new thinking. Strong shear is expected to prevent Sebastien from getting better organized, so gradual weakening is anticipated. The HWRF is once again a notable outlier, as the 06Z run stubbornly forecasts Sebastien to become a hurricane. While not impossible, that scenario appears unlikely and has been discounted. Aside from the HWRF, the dynamical guidance otherwise dissipates Sebastien within about 3 days, and this is reflected in the official forecast. Given Sebastien's shallow and disorganized structure, it is certainly possible that its wind field may become poorly-defined and the system could dissipate sooner than currently forecast. The tropical storm continues to move at a slower pace and to the right of previous forecasts. The initial motion estimate is 075/13 kt. The latest NHC track forecast is slower and to the right of the previous advisory, closer to the global model consensus. The cyclone is expected to continue generally northeastward or east-northeastward near the southern end of an eastward-moving frontal boundary through the weekend or as long as it remains a tropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 25.2N 55.3W 45 KT 50 MPH 12H 23/0000Z 25.8N 53.5W 45 KT 50 MPH 24H 23/1200Z 27.0N 51.3W 45 KT 50 MPH 36H 24/0000Z 28.2N 49.0W 40 KT 45 MPH 48H 24/1200Z 29.3N 46.3W 35 KT 40 MPH 72H 25/1200Z...DISSIPATED $$ Forecaster Zelinsky
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