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Tropical Storm Sebastien Forecast Discussion Number 3
2019-11-20 03:37:12| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Nov 19 2019 000 WTNT45 KNHC 200237 TCDAT5 Tropical Storm Sebastien Discussion Number 3 NWS National Hurricane Center Miami FL AL202019 1100 PM AST Tue Nov 19 2019 There hasn't much of a change with Sebastien for most of tonight, with the center still exposed to the northwest of a large area of deep convection. Recently, the low-level center appears to be slowing down and gaining some latitude as convection re-fires near the center. The initial wind speed will stay 40 kt, pending receipt of ASCAT data later this evening. The initial motion has been more to the west during the past few hours, but a longer-term motion is 290/8. Sebastien should move generally northwestward on Wednesday, northward on Wednesday night and much faster to the northeast on Thursday as the storm moves along the southwestern periphery of the subtropical ridge and then ahead of an approaching mid-latitude trough. The forecast has been adjusted westward in the short-term due mostly to the initial motion, and then eastward in the longer term due to models suggesting the storm may stay a little more ahead of the cold front than before. These forecast changes, however, are fairly typical for a disorganized system. Sebastien has some chance to intensify by late tomorrow as the shear vector and the storm motion vector line up around the same time as the upper-level divergence is forecast to increase. This should cause the cyclone to strengthen, and the new forecast is closely aligned with the previous one. Around 48 hours, Sebastien is expected to become an extratropical cyclone as it is overtaken by a cold front, and then become absorbed by the larger front on Friday. The latest NHC wind speed forecast is close to the model consensus, but below the regional hurricane models. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 20.7N 60.6W 40 KT 45 MPH 12H 20/1200Z 21.5N 61.5W 40 KT 45 MPH 24H 21/0000Z 22.9N 61.5W 45 KT 50 MPH 36H 21/1200Z 24.4N 59.8W 50 KT 60 MPH 48H 22/0000Z 27.2N 56.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 23/0000Z...DISSIPATED $$ Forecaster Blake
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