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WTNT45 KNHC 210258

TCDAT5

 

Hurricane Tammy Discussion Number  11

NWS National Hurricane Center Miami FL       AL202023

1100 PM AST Fri Oct 20 2023



Although the satellite and radar presentations of Tammy do not 

appear to have become significantly better organized, with a small 

CDO and limited convective banding features, reconnaissance 

aircraft data indicate the hurricane has strengthened slightly.  

Dropsonde and SFMR-observed surface winds from Air Force and NOAA 

Hurricane Hunter aircraft support an intensity of 70 kt for this 

advisory.  This is a little above the most recent Dvorak estimates. 



Center fixes from the Hurricane Hunter aircraft indicate that Tammy

is still moving west-northwestward or at about 295/8 kt, so the 

anticipated northwestward turn has not yet occurred.  The hurricane 

is moving along the southwestern periphery of a large subtropical 

high pressure area.  A strong mid-tropospheric trough moving off the 

U.S. east coast should erode the western portion of the ridge and 

cause Tammy to turn northwestward to northward during the next 

couple of days.  However, based on the more westward motion observed 

by the Hurricane Hunters, the official track forecast has been 

shifted somewhat to the west of the previous one through 48 hours.  

This is a little west of the model consensus.  The track guidance is 

not in very good agreement on the movement of Tammy after is passes 

the northern Leeward Islands.  Some of the models, such as the 

ECMWF, show the system moving quite slowly at 72 hours and beyond.  

The GFS is an outlier with a more rapid north-northeastward motion. 

Based on the dynamical model consensus, the NHC track forecast is 

slower than the previous one in the 3- to 5-day time frame.



Tammy should remain in an environment of high oceanic heat content, 

but with moderate vertical wind shear for the next couple of days.  

Thus, some modest strengthening is forecast during the next 24 

hours, while the system passes near or over portions of the Leeward 

Islands.  The NHC intensity forecast is a little higher than the 

previous one, and above the simple and corrected model consensus 

guidance.

 

It should be noted that there is a significant area of deep 

convection well to the south-southeast of the center which 

could bring heavy rains to portions of the Lesser Antilles well 

after the center of the hurricane passes by.



 

KEY MESSAGES:

 

1.  Hurricane conditions are expected in portions of the Leeward

Islands by late tonight through Saturday. Tropical storm

conditions are expected to begin in portions of the Lesser Antilles

within the warning area overnight.

 

2.  Heavy rains from Tammy will affect the Windward and Leeward

Islands into Saturday morning, spreading into the British and U.S.

Virgin Islands and eastern 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  21/0300Z 14.7N  60.2W   70 KT  80 MPH

 12H  21/1200Z 15.8N  61.0W   75 KT  85 MPH

 24H  22/0000Z 17.3N  62.0W   80 KT  90 MPH

 36H  22/1200Z 18.8N  63.0W   80 KT  90 MPH

 48H  23/0000Z 20.0N  63.8W   80 KT  90 MPH

 60H  23/1200Z 21.4N  64.3W   80 KT  90 MPH

 72H  24/0000Z 22.4N  64.0W   75 KT  85 MPH

 96H  25/0000Z 24.0N  62.5W   70 KT  80 MPH

120H  26/0000Z 27.0N  60.0W   65 KT  75 MPH

 

$$

Forecaster Pasch