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WTNT45 KNHC 191501

TCDAT5

 

Tropical Storm Tammy Discussion Number   5

NWS National Hurricane Center Miami FL       AL202023

1100 AM AST Thu Oct 19 2023

 

Tammy is a sheared tropical cyclone with the center located on the 

northwestern edge of the main convective mass.  Despite this 

structure, the storm has strengthened since yesterday. A NOAA 

Hurricane Hunter aircraft that investigated Tammy this morning found 

peak 700-mb flight-level winds of 49 kt and peak SFMR winds of 50 

kt. Based on these data, the intensity was increased to 50 kt on a 

Special advisory that was issued at 1200 UTC.  The plane did not 

find any stronger winds since that time, and the initial intensity 

remains 50 kt for this advisory.  An Air Force Reserve 

reconnaissance aircraft is scheduled to investigate Tammy this 

afternoon. 



Tammy is moving west-northwestward or 285 degrees at 13 kt. The 

storm is forecast to reach the southwestern periphery of a 

subtropical ridge over the central Atlantic by Friday, and this 

should cause Tammy to slow down and turn northwestward during the 

next 24 to 36 hours. This motion is forecast to bring the center of 

the storm near or over portions of the Leeward Islands late Friday 

and Saturday.  After Tammy moves north of the Leeward Islands, the 

storm is expected to turn northward around the western side of the 

ridge.  There is still significant spread on exactly when the 

northwestward turn occurs with the GFS and ECMWF along the right 

side of the guidance envelope, with some of the regional hurricane 

models along the left side.  The NHC track is near the middle of 

the guidance envelope closest to the HFIP corrected consensus 

model. 

 

Tammy will be moving over warm SSTS as it nears the Leeward Islands, 

which should allow for gradual strengthening despite the presence 

of light to moderate wind shear.  Given the current sheared 

structure, the NHC intensity forecast is a bit more conservative 

during the first day or two than much of the intensity guidance.  

Despite that, the updated NHC forecast calls for Tammy to be at or 

near hurricane strength when it moves near or over the Leeward 

Islands.   Additional strengthening is expected after Tammy moves 

north of the Leeward Islands and recurves over the central 

Atlantic. 

 

 

KEY MESSAGES:

 

1.  Tropical storm conditions are expected to begin in portions 

of the Lesser Antilles on Friday, where a tropical storm warning is 

in effect.  Tropical storm and hurricane conditions are possible 

elsewhere in the Leeward Islands where hurricane and tropical storm 

watches are currently in effect. Additional watches and warnings

will likely be required later today.

 

2.  Heavy rains from Tammy will begin to affect the northern

Windward and Leeward Islands on Friday, spreading into the British

and U.S. Virgin Islands and Puerto Rico over the weekend.  This

rainfall may produce isolated flash and urban flooding, along with

isolated mudslides in areas of higher terrain.

 

 

FORECAST POSITIONS AND MAX WINDS

 

INIT  19/1500Z 13.6N  55.7W   50 KT  60 MPH

 12H  20/0000Z 14.0N  57.4W   55 KT  65 MPH

 24H  20/1200Z 14.8N  59.2W   60 KT  70 MPH

 36H  21/0000Z 16.0N  60.9W   60 KT  70 MPH

 48H  21/1200Z 17.5N  62.1W   65 KT  75 MPH

 60H  22/0000Z 19.0N  62.8W   70 KT  80 MPH

 72H  22/1200Z 20.5N  63.3W   70 KT  80 MPH

 96H  23/1200Z 24.0N  62.8W   75 KT  85 MPH

120H  24/1200Z 28.4N  57.9W   75 KT  85 MPH

 

$$

Forecaster Brown