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Hurricane Tammy Discussion Number  18
NWS National Hurricane Center Miami FL       AL202023
500 PM AST Sun Oct 22 2023
 
The core of Tammy continues to pull away from the northern Leeward 
Islands, but a trailing area of heavy rain continues to affect 
portions of the Windward and Leeward Islands.  The NOAA Hurricane 
Hunters found maximum 750-mb flight-level winds of 83 kt and peak 
SFMR winds of around 70 kt.  In addition, the minimum pressure has 
fallen to 988 mb.  These data support nudging the initial intensity 
up to 75 kt.  Tammy continues to have a small central dense 
overcast pattern in satellite images with very cold cloud tops 
evident near the center.  An ASCAT-B pass from a few hours ago was 
helpful in adjusting the 34- and 50-kt wind radii, and it confirmed 
that Tammy remains a relatively compact tropical cyclone.
 
The hurricane is moving northwestward at 8 kt on the southwestern
periphery of a subtropical ridge centered over the central Atlantic.
A turn to the north is forecast to occur late tonight, followed by a
northeastward motion beginning Monday night when a large-scale
trough over the northeast U.S. shifts eastward, eroding the ridge.
After that time, the models show the trough cutting off and merging
with Tammy, which will likely cause a sharp turn to the left.  The
models have come in slightly better agreement in the overall
scenario, and only small changes were made to the previous NHC track
forecast.
 
Tammy will likely fluctuate in strength during the next few days
while it remains over warm SSTs and in a moderate wind shear
environment.  After Tammy merges with the trough, dry air
entrainment and stronger shear should cause weakening and likely
lead to extratropical transition in 3 to 4 days.  The NHC intensity
forecast is similar to the previous one and roughly in the middle
of the guidance envelope.
 
 
KEY MESSAGES:
 
1.  The heaviest rains from Tammy will continue over the Leeward
Islands through tonight.  This rainfall may produce isolated flash
and urban flooding, along with isolated mudslides in areas of higher
terrain.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  22/2100Z 19.9N  63.4W   75 KT  85 MPH
 12H  23/0600Z 20.9N  63.8W   75 KT  85 MPH
 24H  23/1800Z 22.0N  63.6W   80 KT  90 MPH
 36H  24/0600Z 22.8N  62.9W   80 KT  90 MPH
 48H  24/1800Z 23.6N  62.0W   80 KT  90 MPH
 60H  25/0600Z 24.4N  61.0W   80 KT  90 MPH
 72H  25/1800Z 25.8N  60.2W   75 KT  85 MPH
 96H  26/1800Z 28.9N  60.4W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  27/1800Z 30.7N  64.3W   50 KT  60 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Cangialosi
 
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