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Tropical Storm Fred Discussion Number   7
NWS National Hurricane Center Miami FL       AL062021
500 AM AST Wed Aug 11 2021
 
Fred's satellite and radar presentation have changed little since
it became a tropical storm yesterday evening.  The system consists
mainly of a circularly shaped area of deep convection with cloud
tops colder than -70C on infrared images, with some rain bands
trying to wrap around the center on radar images.  The outer
banding features have become indistinct on satellite imagery at the
moment.  Upper-level outflow remains well defined.   Wind gusts to
tropical storm force were reported at elevated sites at Cabo Rojo on
the southwestern tip of Puerto Rico.  The current intensity estimate
is held at 35 kt, in agreement with Advanced Dvorak Technique 
estimates from UW-CIMSS.
 
A west-northwestward motion appears to have resumed, at about 14
kt.  The system should continue to move on this heading with a
gradual decrease in forward speed, on the south side of a mid-level
subtropical ridge, for the next 2-3 days.  Around 72 hours, Fred
should begin to turn to the right as it nears the western periphery
of the ridge.  During the next 3-5 days a generally northwestward
track, toward a weakness in the ridge, is likely.  The official
forecast track is about the same as the previous one, and in good
agreement with the latest TVCA and HCCA model consensus guidance.
Again, users are advised that 4- and 5-day track forecasts have
average errors of 175 and 200 miles, respectively.
 
Although the vertical shear is currently low, which would normally 
be conducive for strengthening, the cyclone will soon begin to 
interact with the land mass of Hispaniola.  This should cause some 
weakening later today and tonight.  Some restrengthening should 
occur after the system moves away from that island. However, given 
the likely disruption of the circulation by the mountains, Fred may 
be slow to regain intensity.  Moreover, an upper-level low and 
trough near Florida in 2-3 days could impart increasing 
west-southwesterly shear and limit intensification. The official 
intensity forecast is close to the model consensus and the LGEM 
guidance.  As usual, there is significant uncertainty in the 
intensity forecast for the latter part of the period.
  
 
KEY MESSAGES:
 
1. Tropical storm conditions are expected to begin in portions of 
the Dominican Republic this morning.  Tropical storm conditions are 
possible in northern Haiti and the southeastern Bahamas by late 
today.
 
2. Heavy rainfall could lead to flash, urban, and small stream
flooding, along with possible rapid river rises and the potential
for mudslides across the U.S. Virgin Islands, Puerto Rico, and the
Dominican Republic. The greatest threat for flooding impacts will be
across eastern and southern Puerto Rico.
 
3. There is a risk of wind and rainfall impacts elsewhere in 
portions of Hispaniola, the Bahamas, and Cuba during the next few 
days, although the forecast is more uncertain than usual since Fred 
is forecast to interact with Hispaniola today.  Interests in these 
areas should monitor Fred's progress and updates to the forecast.
 
4. There is a risk of wind and rainfall impacts in Florida beginning
Friday in the Keys and spreading northward through portions of the
Peninsula and the Panhandle this weekend. However, it is too soon to
determine the exact timing, location, and magnitude of any potential
impacts.  Interests throughout Florida should monitor Fred's 
progress and check updates to the forecast.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  11/0900Z 18.0N  68.2W   35 KT  40 MPH
 12H  11/1800Z 19.0N  70.2W   30 KT  35 MPH...INLAND
 24H  12/0600Z 20.1N  72.5W   30 KT  35 MPH...OVER WATER
 36H  12/1800Z 21.1N  74.7W   35 KT  40 MPH
 48H  13/0600Z 22.1N  77.0W   35 KT  40 MPH
 60H  13/1800Z 23.0N  79.0W   35 KT  40 MPH
 72H  14/0600Z 24.1N  80.7W   40 KT  45 MPH
 96H  15/0600Z 27.0N  83.0W   45 KT  50 MPH
120H  16/0600Z 29.5N  85.0W   55 KT  65 MPH
 
$$
Forecaster Pasch
 
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