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Hurricane Florence Forecast Discussion Number 22
2018-09-04 22:32:33| National Hurricane Center (Atlantic)
Issued at 500 PM AST Tue Sep 04 2018 669 WTNT41 KNHC 042032 TCDAT1 Hurricane Florence Discussion Number 22 NWS National Hurricane Center Miami FL AL062018 500 PM AST Tue Sep 04 2018 Despite being over marginally warm water and in an environment of moderate west-southwesterly shear, Florence's intensity has increased during the day. The hurricane has a cloud-filled eye in visible imagery, and the central dense overcast is becoming more symmetric. Based on Dvorak estimates of T4.5 from TAFB and SAB, and a SATCON estimate of 77 kt, the initial intensity is now, somewhat surprisingly, 75 kt. Since the current intensification trend may not be over, the official forecast calls for Florence to strengthen just a little more during the next 6-12 hours. Even though the hurricane will be moving over progressively warmer waters, increasing vertical shear and dry air in the middle levels of the atmosphere should induce some weakening in the 24-72 hour time frame. Lower shear after 72 hours will likely allow Florence to regain hurricane strength by the end of the forecast period. The NHC intensity forecast is primarily adjusted to account for the recent strengthening trend, and is closest to the Florida State Superensemble and HCCA guidance. Florence remains on a west-northwestward course at 300/10 kt. This trajectory is expected to continue through 36 hours while the hurricane remains near the southwestern edge of the subtropical ridge. After 36 hours, Florence is expected to turn northwestward and slow down as it enters a break in the ridge. The track models are in good agreement and show little spread through 48 hours. On days 3-5, the biggest outlier is the UKMET, which lies to the south of the guidance suite. In fact, the bulk of the models, including the deterministic GFS and ECMWF, are all now showing a more definitive poleward motion by day 5. While the official NHC track forecast reflects this thinking, there is still considerable spread among the associated global model ensembles, and the longer-term forecast should be considered low confidence. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 20.3N 43.2W 75 KT 85 MPH 12H 05/0600Z 21.0N 44.8W 80 KT 90 MPH 24H 05/1800Z 22.1N 46.8W 75 KT 85 MPH 36H 06/0600Z 23.2N 48.7W 65 KT 75 MPH 48H 06/1800Z 24.3N 50.4W 60 KT 70 MPH 72H 07/1800Z 26.0N 53.0W 55 KT 65 MPH 96H 08/1800Z 27.5N 55.0W 60 KT 70 MPH 120H 09/1800Z 29.5N 56.5W 70 KT 80 MPH $$ Forecaster Berg
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