####018003347####
WTNT45 KNHC 220259

TCDAT5

 

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