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Hurricane Dorian Forecast Discussion Number 24
2019-08-30 10:54:55| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Aug 30 2019 000 WTNT45 KNHC 300854 TCDAT5 Hurricane Dorian Discussion Number 24 NWS National Hurricane Center Miami FL AL052019 500 AM AST Fri Aug 30 2019 There hasn't been a lot of new data since the Hurricane Hunter planes departed Dorian several hours ago. The convective pattern on infrared satellite imagery has been nearly steady state, although the latest Dvorak estimates from TAFB and SAB rose to T5.0/90 kt. These estimates, combined with the earlier aircraft data, support maintaining an initial intensity of 90 kt. Dorian's heading is very gradually turning toward the left, with the latest estimate northwestward, or 320 degrees at 10 kt. Dorian is now being steered between a mid-tropospheric high centered near Bermuda and a mid-/upper-level low located over the Bahamas. The high is expected to expand westward, with a blocking ridge becoming established over the western Atlantic during the next several days. With the exception of COAMPS-TC and HMON, the other reliable models are in excellent agreement through day 3, with Dorian turning westward south of the ridge and moving near or over the northernmost islands in the Bahamas Sunday and Monday. After day 3, steering currents collapse as a break develops in the ridge, and Dorian will likely slow down considerably as it approaches the Florida peninsula. There is more spread among the deterministic models and their ensemble members during that time, with disagreement on exactly when and where Dorian will turn northwestward and northward on days 4 and 5. That being said, the tracks of the simple and corrected consensus models on this cycle did not warrant much change to the official NHC forecast, with perhaps just a slight southward adjustment on days 3 and 4. The biggest concern will be Dorian's slow motion when it is near Florida, placing some areas of the state at an increasing risk of a prolonged, drawn-out event of strong winds, dangerous storm surge, and heavy rainfall. The upper-level low to the west of Dorian continues to impart some southwesterly shear over the hurricane, which has prevented it from strengthening rapidly. However, Dorian is expected to enter a more favorable upper-level environment during the next 24 hours, which should allow its structure to become more well developed. Although overall the environment ahead of the storm appears conducive for strengthening, some models (in particular the ECMWF) suggest that some northerly shear could come into play while Dorian moves through the northwestern Bahamas, and for that reason the NHC official intensity forecast is not quite as bullish as the HCCA, Florida State Superensemble, and HWRF models. Still, Dorian is forecast to become a dangerous major hurricane later and maintain that status as it heads for the northwestern Bahamas and the Florida peninsula. Key Messages: 1. A Hurricane Watch is now in effect for the northwestern Bahamas, where the risk of life-threatening storm surge and hurricane-force winds this weekend has continued to increase. Residents should begin to execute their hurricane plans and listen to advice given by local emergency officials. 2. There is an increasing likelihood of a prolonged period of hazardous weather conditions that could last for a couple of days in parts of Florida early next week. 3. The risk of life-threatening storm surge along portions of the Florida east coast has increased, although it is too soon to determine where the highest storm surge will occur. The risk of devastating hurricane-force winds along the Florida east coast and peninsula early next week has also increased, although it is too soon to determine where the strongest winds will occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 4. Regardless of the exact track of Dorian, heavy rains are expected to occur over portions of the Bahamas, Florida, and elsewhere in the southeastern United States this weekend and into the middle of next week. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 23.8N 69.1W 90 KT 105 MPH 12H 30/1800Z 24.8N 70.3W 100 KT 115 MPH 24H 31/0600Z 25.6N 72.0W 105 KT 120 MPH 36H 31/1800Z 26.1N 73.8W 110 KT 125 MPH 48H 01/0600Z 26.4N 75.5W 115 KT 130 MPH 72H 02/0600Z 26.7N 78.3W 120 KT 140 MPH 96H 03/0600Z 26.9N 80.1W 115 KT 130 MPH...INLAND 120H 04/0600Z 28.1N 81.4W 65 KT 75 MPH...INLAND $$ Forecaster Berg
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