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Hurricane Tammy Discussion Number  15
NWS National Hurricane Center Miami FL       AL202023
1100 PM AST Sat Oct 21 2023
 
Air Force and NOAA Hurricane Hunter aircraft data, along with radar
imagery from Guadeloupe, indicate that the center of Tammy passed
over the island of Barbuda a couple of hours ago.  The hurricane
continues to produce intense convection in a small CDO feature with
some ill-defined bands north and northeast of the center.  The
eyewall has generally not been closed on the radar images.  There
are still some areas of strong convection affecting portions of the
Lesser Antilles to the south of Tammy.  Flight-level and SFMR winds
along with Doppler velocity data suggested that the maximum winds 
had decreased slightly, but there was an unofficial report of a 
sustained wind of 78 kt from Barbuda.  Based on a blend of the 
aircraft data and the Barbuda observation, the intensity is held at 
75 kt for this advisory.

Center fixes indicate that the hurricane continues on its 
north-northwestward trek with an estimated motion of 330/9 kt. Over 
the next couple of days, Tammy should turn northward while it moves 
along the western side of a large subtropical high.  Then, the 
system should turn, at least temporarily, northeastward on the 
southeastern periphery of a mid-tropospheric trough over the western 
Atlantic.  Beginning around 3 days, the track forecast becomes 
challenging, since the global models indicate that the western 
Atlantic trough will bypass Tammy after 72 hours while it continues 
eastward.  A ridge could then build in to the northwest of the 
system and cause it to turn to the left.  As noted earlier, there is 
a very large spread in the track guidance in the latter part of the 
forecast period.  There is low confidence in the 4- and 5-day NHC 
forecast positions.
 
Tammy should remain over very warm waters with moderate vertical
wind shear for the next couple of days.  So, some slight 
strengthening is still forecast.  By 60 or 72 hours, increasing 
shear is likely to induce a weakening trend.  The official intensity 
forecast is similar to the latest Decay-SHIPS guidance.
 
 
KEY MESSAGES:
 
1.  Hurricane and tropical storm conditions are expected in portions
of the northern Leeward Islands through early Sunday.
 
2.  The heaviest rains from Tammy will continue over the Leeward
Islands through Sunday. This rainfall may produce isolated flash and
urban flooding, along with isolated mudslides in areas of higher
terrain.
 
3.  A storm surge could produce coastal flooding in areas of onshore
winds as the center of Tammy moves near or over the Leeward Islands.
Near the coast, the surge will be accompanied by large and dangerous
waves.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  22/0300Z 17.8N  61.9W   75 KT  85 MPH
 12H  22/1200Z 18.8N  62.5W   75 KT  85 MPH
 24H  23/0000Z 20.2N  63.4W   80 KT  90 MPH
 36H  23/1200Z 21.5N  63.9W   80 KT  90 MPH
 48H  24/0000Z 22.6N  63.8W   80 KT  90 MPH
 60H  24/1200Z 23.1N  63.6W   80 KT  90 MPH
 72H  25/0000Z 23.5N  63.0W   75 KT  85 MPH
 96H  26/0000Z 25.0N  62.5W   70 KT  80 MPH
120H  27/0000Z 27.5N  63.5W   60 KT  70 MPH
 
$$
Forecaster Pasch
 
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