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Tropical Storm Florence Forecast Discussion Number 20
2018-09-04 10:38:28| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Sep 04 2018 770 WTNT41 KNHC 040838 TCDAT1 Tropical Storm Florence Discussion Number 20 NWS National Hurricane Center Miami FL AL062018 500 AM AST Tue Sep 04 2018 Florence's cloud pattern has changed very little during the past several hours, with the exception of a possible small Central Dense Overcast developing just to the east of the center. An earlier AMSR2 overpass revealed a rather obvious tilt toward the east-northeast, indicative of the moderate southwesterly shear. The initial intensity is held a 60 kt, and is supported by the Dvorak subjective and objective T-numbers. Florence should exhibit little change in strength during the next 24 hours or so, as the cyclone traverses marginally warm sea surface temperatures and is influenced by modest west-southwesterly shear. Slight weakening is expected during the mid- forecast period as the shear gradually increases with time. Afterward, the upper-level wind environment should become a little more favorable and, at the same time, Florence will be moving back over warmer SSTs. Consequently, the cyclone should gradually strengthen through day 5. This forecast is unchanged from the previous one, and is in good agreement with the NOAA-HCCA guidance. The initial motion estimate is west-northwestward, or 290/11 kt. The cyclone is expected to be steered west-northwestward for the next 48 hours by a mid- to upper tropospheric ridge anchored to the north, followed by a northwestward turn around the 72 hr period as it enters a growing weakness in the aforementioned ridge. A rather large spread in the global and hurricane models remains particularly beyond day 4, however, the consensus models and the global ensemble means have have been fairly consistent from run to run. This forecast is just a bit to the north of the previous advisory and just south of the consensus models. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 19.3N 42.0W 60 KT 70 MPH 12H 04/1800Z 19.9N 43.7W 60 KT 70 MPH 24H 05/0600Z 20.8N 45.8W 60 KT 70 MPH 36H 05/1800Z 21.8N 48.0W 55 KT 65 MPH 48H 06/0600Z 22.9N 50.2W 50 KT 60 MPH 72H 07/0600Z 25.2N 53.4W 50 KT 60 MPH 96H 08/0600Z 27.1N 55.6W 55 KT 65 MPH 120H 09/0600Z 29.1N 57.7W 65 KT 75 MPH $$ Forecaster Roberts
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