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Tropical Storm Dorian Forecast Discussion Number 14
2019-08-27 23:00:25| National Hurricane Center (Atlantic)
Issued at 500 PM AST Tue Aug 27 2019 000 WTNT45 KNHC 272100 TCDAT5 Tropical Storm Dorian Discussion Number 14 NWS National Hurricane Center Miami FL AL052019 500 PM AST Tue Aug 27 2019 Dorian's convective pattern has continued to fluctuate this afternoon due to some interaction with the Windward and Leeward Islands, but mainly due to intrusions of very dry mid-level air. A 10-mile wide eye feature developed in Martinique and Guadeloupe radar data between 1500-1600 UTC and again between 1700-1800 UTC. But this feature had been short-lived due to erosion of the inner-core convection caused by dry air entrainment, although a recent burst of deep convection has developed near and over the low-level center. Dorian's upper-level outflow has continued to expand and is very symmetrical. The initial intensity has been maintained at 45 kt based on earlier aircraft flight-level and SFMR surface wind data. Despite the center redeveloping farther north, radar and recon fixes indicate that the motion remains west-northwestward or 300/11 kt. Due to the more northward initial position, the new forecast track was shifted 30-60 n mi northeast of the previous one track through 96 hours. The global models are in good agreement on Dorian moving west-northwestward tonight and then turning northwestward on Wednesday, bringing the cyclone's center near or over the central or western portions of Puerto Rico. After clearing the island by early Thursday, Dorian is forecast to move cyclonically around the eastern portion of a southwestward-moving mid/upper-level low on days 3-5. The evolution of the upper-low and how strong the mid-level ridge to the north builds in behind the low and across the southeastern U.S. will determine when and how sharp Dorian's turn back the west-northwest will occur. The new NHC track is close to a blend consensus models TVCN, HCCA, and FSSE, and brings Dorian near the east-central Florida coast in 120 hours. Users are reminded not to focus on the details of the extended track forecast as the average 5-day track error is around 200 miles. Dry air should continue to plague Dorian for the next 24 hours or so, resulting in only slow strengthening. Land interaction with Puerto Rico should significantly weaken the small cyclone, thus the intensities were lowered at 36 and 48 hours. On days 3-5, the models continue to indicate that the upper-level flow pattern and shear conditions should favor strengthening, especially since Dorian will be moving over SSTs greater than 29 deg C and into a moist mid-level environment. The dynamical models such as the GFS, UKMET, and ECMWF are now showing more strengthening than previous runs, but still remain well below the statistical SHIPS and LGEM intensity models, which bring Dorian to category 1 or 2 strength by day 5. The official intensity forecast remains a compromise between the these two extremes, and is close to the HCCA and FSSE consensus models. Given the large spread in the guidance, there remains lower-than- normal confidence in the intensity forecast, especially on days 4 and 5. Key Messages: 1. Tropical storm conditions are expected in the U.S. Virgin Islands and Puerto Rico on Wednesday and in portions of the Dominican Republic Wednesday night and Thursday. Hurricane conditions are possible in Puerto Rico and portions of the Dominican Republic. 2. Heavy rainfall over portions of Puerto Rico and the Dominican Republic could produce flash flooding during the next few days. Heavy rains are expected to occur over portions of the Bahamas and Florida later this week and into early next week. 3. The threat of tropical storm or hurricane conditions, along with storm surge, in the Bahamas and along portions of the Florida east coast have increased. Residents in these areas should monitor the progress of Dorian and ensure that they have their hurricane plan in place. 4. Uncertainty in the intensity forecast later this week remains higher than usual due to the potential for Dorian's interaction with Puerto Rico and Hispaniola to weaken the storm. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 15.3N 62.5W 45 KT 50 MPH 12H 28/0600Z 16.2N 64.1W 50 KT 60 MPH 24H 28/1800Z 17.6N 66.2W 55 KT 65 MPH 36H 29/0600Z 19.1N 67.8W 40 KT 45 MPH 48H 29/1800Z 20.8N 69.2W 45 KT 50 MPH 72H 30/1800Z 24.2N 72.2W 55 KT 65 MPH 96H 31/1800Z 26.7N 76.1W 60 KT 70 MPH 120H 01/1800Z 28.2N 80.6W 60 KT 70 MPH...NEAR THE FLORIDA COAST $$ Forecaster Stewart
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