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Potential Tropical Cyclone Six Discussion Number   5...Corrected
NWS National Hurricane Center Miami FL       AL062021
500 PM AST Tue Aug 10 2021

Corrected speed of motion in second paragraph.

Satellite imagery this afternoon continues to show that the 
disturbance has an organized convective pattern, with satellite 
intensity estimates of tropical-storm strength from SAB and TAFB. 
However, the circulation still appears to not be well defined, with 
the San Juan WSR-88D Doppler radar showing multiple mid-level 
centers and several convective cells with small-scale rotation. 
Based on this, the system will not be upgraded to a tropical cyclone 
at this time.  The initial intensity remains 30 kt based on mainly 
on continuity from earlier data.  It should be noted that squalls 
with short-lived winds to tropical-storm force have been reported in 
bands over the northern Leeward Islands.
 
The initial motion remains west-northwestward or 295/15 kt.  A
strong low- to mid-level ridge to the north should steer the system
generally west-northwestward for the next 72 h with some decrease in
forward speed after 24 h.  Beyond that time, a turn toward the
northwest with an further decrease in forward speed is likely while
the system moves near the western periphery of the ridge.  There
has been some increase in the spread of the track guidance from
72-120 h, with the GFS shifting to the right and the other models
not changing very much.  The new NHC forecast track has only minor
changes from the previous one and lies near the various consensus
models.
 
Conditions continue to appear favorable for strengthening before the
system reaches Hispaniola in about 18 h, although there may be dry
air entraining into the system in the southeastern quadrant.  The
intensity forecast will follow the previous prediction in calling
for the disturbance to become a tropical storm before landfall,
followed by weakening to a depression. From 24-60 h, the models
have come into better agreement that the system will encounter
westerly vertical wind shear, and based on that and the possibility 
of land interaction the intensity forecast shows little
re-intensification during that time.  After 60 h, the models still
disagree on the evolution of the upper-level winds near the system,
but they are in better agreement that conditions over the eastern
Gulf will become more conducive for development.  Thus, the
intensity forecast calls for intensification during that time.  The
new intensity forecast is almost the same as the previous one.
 
KEY MESSAGES:
 
1. The system is forecast to become a tropical storm as it moves
over the northeastern Caribbean Sea tonight.  Tropical storm
conditions are expected in portions of the U.S. Virgin Islands and
Puerto Rico tonight, and are expected to begin in the Dominican
Republic by Wednesday.  Tropical storm conditions are possible in
northern Haiti and the southeastern Bahamas by late Wednesday.
 
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 the eastern and southern portions of Puerto Rico.
 
3. There is a risk of wind and rainfall impacts elsewhere in 
portions of Hispaniola, the Bahamas, and Cuba during the next 
several days, although the forecast is more uncertain than usual 
since the system is still in its formative stage. Interests in these 
areas should monitor the system's progress and updates to the 
forecast.
 
4. There is a risk of wind and rainfall impacts in portions of 
Florida beginning Friday through the weekend. However, given the 
uncertainty in the long-range forecast it is too soon to determine 
the timing, location, and magnitude of any potential impacts. 
Interests in Florida should monitor updates to the forecast. 

FORECAST POSITIONS AND MAX WINDS
 
INIT  10/2100Z 16.9N  65.5W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
 12H  11/0600Z 17.8N  67.8W   35 KT  40 MPH...TROPICAL CYCLONE
 24H  11/1800Z 19.0N  70.4W   35 KT  40 MPH...INLAND
 36H  12/0600Z 20.2N  72.8W   30 KT  35 MPH...OVER WATER
 48H  12/1800Z 21.2N  75.0W   30 KT  35 MPH
 60H  13/0600Z 22.1N  77.2W   35 KT  40 MPH
 72H  13/1800Z 23.1N  79.1W   35 KT  40 MPH
 96H  14/1800Z 25.5N  82.5W   40 KT  45 MPH
120H  15/1800Z 28.5N  84.5W   50 KT  60 MPH
 
$$
Forecaster Beven
 
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