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Tropical Storm Dorian Forecast Discussion Number 13
2019-08-27 17:13:22| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Aug 27 2019 000 WTNT45 KNHC 271512 CCA TCDAT5 Tropical Storm Dorian Discussion Number 13...Corrected NWS National Hurricane Center Miami FL AL052019 1100 AM AST Tue Aug 27 2019 Corrected southeastward to southwestward motion in third paragraph Dorian moved directly across the center of St. Lucia around 1000 UTC, which resulted in a significant disruption of the small inner-core wind field. An Air Force Reserve reconnaissance aircraft had difficulty identifying a clear-cut center and radar data from Martinique indicates that the mid-level circulation has also been disrupted somewhat. Having said that, the overall appearance of the cyclone in both satellite and radar imagery has improved since this time yesterday, although a pronounced dry slot is now evident in the southeastern quadrant of the circulation. The initial intensity of 45 kt is being maintained based on aircraft flight-level and SFMR surface wind data. The initial motion remains west-northwestward or 295/11 kt. There is still no significant change to the previous forecast track or reasoning. Although the inner-core wind field and low-level center have been disrupted, the overall circulation envelope has remained intact and is expected to move west-northwestward to northwestward for the next 36-48 hours toward a break in the subtropical ridge located well north of Dorian. The mid- to upper-level low currently located east of the Bahamas that has weakened the ridge is forecast to gradually weaken while digging southwestward across the central Bahamas and toward central Cuba over the next 3-4 days, resulting in Dorian turning northwestward on day 3 before turning back toward the west-northwest on days 4 and 5. How quickly the west-northwestward turn occurs will depend heavily on the evolution of the upper-low. For now, the previous forecast track remains unchanged other than to push out the track a little northeastward at 48 and 72 hours. The NHC model guidance remains tightly packed and in good agreement on this scenario, and the new forecast track lies very close to an average of the various consensus track models. 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 continues to plague Dorian, and interaction with the mountainous terrain of St. Lucia will likely hinder significant development in the short term. However, the models continue to indicate that the upper-level flow pattern and shear conditions are expected to remain favorable for strengthening throughout the forecast period, so it is uncertain why the dynamical models are not showing more development and strengthening when compared to the more robust statistical SHIPS intensity models, especially at days 4 and 5 when Dorian will be moving over SSTs greater than 29 deg C and into a fairly moist environment. For now, the official intensity forecast remains basically midway between the stronger SHIPS model and the much weaker global and regional models. Given the large spread in the guidance, there is lower than normal confidence in the intensity forecast, especially on days 4 an 5. Key Messages: 1. Tropical storm conditions will continue in portions of the Lesser Antilles during the next several hours. Tropical storm conditions are expected and hurricane conditions are possible in Puerto Rico on Wednesday and in portions of the Dominican Republic Wednesday night and Thursday. 2. Heavy rainfall over portions of the Lesser Antilles, Puerto Rico, and the Dominican Republic could produce flash flooding during the next few days. 3. The threat of winds and heavy rains later this week into this weekend in the Turks and Caicos, the Bahamas, and Florida is increasing. 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 Dorian's potential interaction with Hispaniola and Puerto Rico. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 14.2N 61.8W 45 KT 50 MPH 12H 28/0000Z 15.2N 63.4W 50 KT 60 MPH 24H 28/1200Z 16.5N 65.5W 55 KT 65 MPH 36H 29/0000Z 17.9N 67.4W 60 KT 70 MPH 48H 29/1200Z 19.5N 69.0W 60 KT 70 MPH 72H 30/1200Z 22.8N 72.0W 55 KT 65 MPH 96H 31/1200Z 25.6N 76.0W 60 KT 70 MPH 120H 01/1200Z 27.8N 80.4W 60 KT 70 MPH $$ Forecaster Stewart
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