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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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