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Tropical Depression Five Discussion Number   2
NWS National Hurricane Center Miami FL       AL052021
1100 PM AST Wed Jun 30 2021
 
The satellite presentation of the system over the last 6-12 hours
has continued to gradually improve, with a prominent banding feature
to the west of the estimated center. An ASCAT-A pass received at
2323 UTC revealed that the low-level circulation has become a bit
better defined compared to earlier today, though still somewhat
elongated to the south and west. The peak wind retrievals from this
instrument were 30-32 kt. While subjective satellite estimates
from TAFB and SAB were a bit higher, the latest estimated intensity
was held at 30 kt for this advisory in agreement with the slightly
lower scatterometer data.
 
The initial motion has accelerated a bit tonight at 280/20
kt. A strong subtropical ridge is situated poleward of the tropical
depression and this feature should steer the system quickly to the
west-northwest over the next several days. After 72 hours, the
tropical cyclone will reach the westward extent of the ridge and
begin to move more poleward and slow down as the ridge also becomes
eroded by a mid-latitude trough to over the eastern US. The track
guidance in the latter portion of the forecast continues to exhibit
large spread, with the GFS and HWRF/HMON models along the left side
of the guidance envelop, while the ECMWF and its ensemble mean
on the right side. The latest NHC track forecast is a shade right
of the previous one, and also slightly faster, but given the spread
in the models, the latter portion of the track is more uncertain
than usual.
 
While the depression is currently in a favorable environment of low
vertical wind shear, warm sea-surface temperatures, and high
mid-level relative humidity, the expected acceleration in forward
motion could cause the system to outrun the favorable upper-level
easterlies currently overhead, after 36 hours. In addition, the
system could be near or over some of the Greater Antilles in the 
latter portions of the forecast. For these reasons, the intensity 
remained capped at 50 kt after 36 hours, and is still on the lower 
end of the intensity guidance suite, though this forecast could be 
somewhat conservative.
 
 
Key Messages:
 
1. The tropical depression is expected to become a tropical storm
before reaching the Lesser Antilles and tropical storm conditions
are expected beginning late Thursday night in portions of the 
Windward and southern Leeward Islands.
 
2. Heavy rainfall will move quickly across the Windward and southern
Leeward Islands, including Barbados, on Friday.  Isolated flash
flooding and mudslides are possible.
 
3. There is a risk of wind and rainfall impacts in portions of the
Virgin Islands, Puerto Rico, Hispaniola, Cuba, the Turks and Caicos
and the southeastern Bahamas through early next week. Interests in 
these areas should monitor the system's progress and updates to the 
forecast.
 
4. Interests in Florida should monitor updates to the forecast for
this system, but it is too soon to determine what if any impacts
could occur there next week given the uncertainty in the long-range
forecast.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  01/0300Z  9.6N  46.3W   30 KT  35 MPH
 12H  01/1200Z 10.5N  49.6W   40 KT  45 MPH
 24H  02/0000Z 11.7N  54.4W   45 KT  50 MPH
 36H  02/1200Z 13.0N  59.6W   50 KT  60 MPH
 48H  03/0000Z 14.7N  65.0W   50 KT  60 MPH
 60H  03/1200Z 16.5N  69.8W   50 KT  60 MPH
 72H  04/0000Z 18.3N  73.8W   50 KT  60 MPH...NEAR THE COAST
 96H  05/0000Z 20.9N  78.6W   50 KT  60 MPH...NEAR THE COAST
120H  06/0000Z 24.5N  82.0W   50 KT  60 MPH...OVER WATER
 
$$
Forecaster Papin/Brown
 
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