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Tropical Depression Fred Forecast Discussion Number 10
2021-08-12 04:52:10| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Wed Aug 11 2021 409 WTNT41 KNHC 120252 TCDAT1 Tropical Depression Fred Discussion Number 10 NWS National Hurricane Center Miami FL AL062021 1100 PM EDT Wed Aug 11 2021 The center of Fred is estimated to be located over extreme eastern Haiti. This position is based on continuity with the previous forecast and a small low-level cyclonic circulation noted in cloud-drift wind vectors that were based on the last few GOES-16 high-resolution visible satellite images. A NOAA reconnaissance aircraft performed a quasi-synoptic surveillance mission this evening and released dropsondes while circumnavigating Hispaniola. Some of the dropsondes measured surface winds of 24-27 kt about 150 nmi north and northwest (in the Windward Passage) of the center, and these data support maintaining an intensity of 30 kt for this advisory. The main convective cloud mass has been displaced to the southeast of the low-level center due to the west-northwesterly vertical wind shear of about 20 kt. The initial motion estimate is 300/13 kt. The global and regional models remain in surprisingly good agreement on Fred maintaining a steady west-northwestward motion through 48-60 hours as a strong ridge remains entrenched over the western Atlantic during that time period. Thereafter, however, the NHC model guidance diverges significantly, with the now much weaker HWRF model taking Fred more westward, while the GFS and ECMWF models move the cyclone northwestward over the eastern Gulf of Mexico near or just offshore the Florida west coast; the UKMET model lies between these two track extremes. The weaker HWRF track has been discounted given the NHC forecast that Fred will remain vertically coherent and restrengthen after moving back over water. Thus, the new NHC track forecast is essentially just an update of the previous advisory track, and lies close to the NOAA-HCCA corrected-consensus model. NOTE: the aforementioned NOAA WP-3D reconnaissance aircraft has been releasing dropsondes from approximately the 450-mb level and has also been collecting tail-Doppler radar data. These data should have been assimilated into the 0000 UTC model runs, which hopefully will provide better track and intensity model forecasts for the next advisory package. Fred is forecast remain within a moderate to strong westerly to southwesterly vertical wind shear regime throughout the forecast period by almost all of the global and regional models. As a result, rapid strengthening is not expected after Fred moves back over water. There is one caveat, however, and that is the ECMWF model forecasting the shear to weaken to 5-10 kt during the 36-72 hour period, which could allow for a little more strengthening than what the official forecast is currently indicating. The new NHC intensity prediction is identical to the previous one owing to the expectation that some degree of westerly shear will be affecting Fred throughout the entire forecast period. The official forecast follows a blend of the IVCN and HCCA consensus intensity models. KEY MESSAGES: 1. Through early Thursday morning, heavy rainfall could lead to flash, urban, and small stream flooding, along with possible rapid river rises and potential mudslides in the Dominican Republic. 2. Tropical storm conditions are possible in northern Haiti, the Turks and Caicos, and the southeastern Bahamas tonight, and in portions of Cuba Thursday. 3. Beginning Friday, heavy rainfall could lead to areal, urban, and small stream flooding, and possible rapid river rises across southern Florida. Heavy rainfall associated with Fred will impact the remainder of Florida and parts of the Southeast this weekend and into next week. 4. There is a risk of tropical storm conditions beginning early Saturday in the Florida Keys and spreading northward along portions of the Florida west coast and the Florida Panhandle through Monday. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 19.5N 72.2W 30 KT 35 MPH...INLAND HISPANIOLA 12H 12/1200Z 20.4N 73.9W 30 KT 35 MPH...OVER WATER 24H 13/0000Z 21.6N 76.1W 30 KT 35 MPH 36H 13/1200Z 22.5N 78.1W 35 KT 40 MPH 48H 14/0000Z 23.5N 79.8W 35 KT 40 MPH 60H 14/1200Z 24.7N 81.2W 40 KT 45 MPH 72H 15/0000Z 26.2N 82.4W 45 KT 50 MPH 96H 16/0000Z 29.2N 84.2W 50 KT 60 MPH 120H 17/0000Z 31.7N 84.7W 35 KT 40 MPH...INLAND $$ Forecaster Stewart
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