####018003777####
WTNT45 KNHC 201459

TCDAT5

 

Hurricane Tammy Discussion Number   9

NWS National Hurricane Center Miami FL       AL202023

1100 AM AST Fri Oct 20 2023

 

Recent data from both NOAA and Air Force Reserve Hurricane Hunter

aircraft and radar imagery from Barbados shows that the inner core

structure of the storm has become much better organized this

morning. The radar imagery has depicted strong convection that has

quickly evolved into a curved band, and more recently a closed eye. 

The aircraft data indicates that there is still some tilt to the 

circulation, but the most recent center fixes indicate that the 

pressure has fallen quickly to around 992 mb this morning.  The 

plane has reported flight-level winds of 71 kt at 700 mb, and SFMR 

values of 65-70 kt.  Based on these data, the initial intensity has 

been increased to 65 kt for this advisory, making Tammy a hurricane.

 

Tammy is moving slowly west-northwestward at about 6 kt. The storm 

should turn northwestward later today as an amplified trough moving 

off the east coast of the U.S. and into the western Atlantic erodes 

the western portion of a subtropical ridge over the central 

Atlantic. This motion is expected to bring the center of Tammy near 

or over portions of the Leeward Islands tonight and Saturday. The 

latest track prediction is similar to the previous advisory and 

lies closest to the HFIP corrected consensus during the first 

36-48 hours.  After Tammy moves north of the Leeward Islands, the 

storm is forecast to turn northward and then begin to recurve in 

the mid-latitude westerlies by days 4 and 5. There is increasing 

along-track spread in the guidance after 72 hours due to how fast 

Tammy accelerates northeastward.  Much of the guidance has been 

trending slower, and the official forecast has followed suit. 



The environment consisting of warm SSTs and light to moderate 

shear favors some additional strengthening during the next couple of 

days. The updated NHC intensity forecast calls for strengthening 

during the next 36-48 hours while Tammy approaches the Leeward 

Islands. Once Tammy is north of the Leeward Islands, increasing 

vertical wind shear is likely to limit additional intensification.  

Near the end of the period, Tammy is likely to begin its 

extratropical transition, but it is still shown to be a hurricane 

at day 5. 



 

KEY MESSAGES:

 

1.  Hurricane conditions are expected in portions of the Leeward 

Islands by late tonight or Saturday morning. Tropical storm 

conditions are expected to begin in portions of the Lesser Antilles 

within the warning area later today.  

 

2.  Heavy rains from Tammy will begin to affect the Leeward and 

northern Windward Islands later today and into Saturday morning, 

spreading into the British and U.S. Virgin Islands and Puerto Rico 

as early as 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  20/1500Z 14.1N  58.6W   65 KT  75 MPH

 12H  21/0000Z 15.1N  59.8W   70 KT  80 MPH

 24H  21/1200Z 16.4N  60.9W   75 KT  85 MPH

 36H  22/0000Z 17.9N  61.9W   75 KT  85 MPH

 48H  22/1200Z 19.3N  62.7W   80 KT  90 MPH

 60H  23/0000Z 20.6N  63.3W   80 KT  90 MPH

 72H  23/1200Z 22.0N  63.3W   80 KT  90 MPH

 96H  24/1200Z 24.4N  61.4W   80 KT  90 MPH

120H  25/1200Z 28.2N  57.7W   75 KT  85 MPH

 

$$

Forecaster Brown