####018003253####
WTNT45 KNHC 221435

TCDAT5

 

Hurricane Tammy Discussion Number  17

NWS National Hurricane Center Miami FL       AL202023

1100 AM AST Sun Oct 22 2023

 

Tammy is slowly pulling away from the northern Leeward Islands and

all of the hurricane warnings were dropped at the 1200 UTC

intermediate advisory.  However, there is still a trailing area of

showers and thunderstorms that will likely cause heavy rain across

portions of the Windward and Leeward Islands throughout the day.

The hurricane is exhibiting a central dense overcast pattern in

satellite images with very cold cloud tops persisting near the

center.  Both the NOAA and Air Force Hurricane Hunters are

investigating Tammy, and based on the data they have collected, the

initial intensity is nudged downward slightly to 70 kt.  Tammy

remains a fairly compact and asymmetric tropical cyclone with

hurricane-force and tropical-storm-force winds only extending up to

20 n mi and 120 n mi from the center, respectively.  The wind radii

are particularly small on the southwest side of the system.

 

The hurricane is moving northwestward at 8 kt on the southwestern

periphery of a subtropical ridge centered over the central Atlantic.

A turn to the north is forecast to occur tonight, followed by a

northeastward motion on Tuesday and Wednesday when a large-scale

trough over the northeast U.S. shifts eastward, eroding the ridge.

After that time, the models show the trough cutting off and merging

with Tammy, which could cause a turn to the left.  Although the

models are in better agreement than they were yesterday, there is

still a considerable amount of spread at long range due to

differences in the synoptic pattern and model predicted intensity

of Tammy.  Only small changes were made to the previous NHC track

forecast, and it continues to lie close to the HCCA guidance.

 

The environmental factors for Tammy appear to be mixed.  The system

is expected to remain over warm SSTs during at least the next few

days, but it will also be in an environment of moderate vertical

wind shear.  Therefore, fluctuations in strength seem likely over

the next few days.  After Tammy merges with the trough, dry air

entrainment and stronger shear should cause some weakening and

likely lead to extratropical transition in 4 to 5 days.  The NHC

intensity forecast is a little lower than the previous one, and near

the middle of the guidance envelope.

 

 

KEY MESSAGES:

 

1.  The heaviest rains from Tammy will continue over the Leeward

Islands through tonight.  This rainfall may produce isolated flash

and urban flooding, along with isolated mudslides in areas of higher

terrain.

 

 

FORECAST POSITIONS AND MAX WINDS

 

INIT  22/1500Z 19.1N  63.0W   70 KT  80 MPH

 12H  23/0000Z 20.1N  63.6W   70 KT  80 MPH

 24H  23/1200Z 21.4N  63.9W   75 KT  85 MPH

 36H  24/0000Z 22.3N  63.5W   75 KT  85 MPH

 48H  24/1200Z 23.0N  62.9W   75 KT  85 MPH

 60H  25/0000Z 23.6N  62.0W   75 KT  85 MPH

 72H  25/1200Z 24.5N  61.0W   75 KT  85 MPH

 96H  26/1200Z 27.5N  60.5W   65 KT  75 MPH

120H  27/1200Z 30.0N  63.9W   55 KT  65 MPH...POST-TROP/EXTRATROP

 

$$

Forecaster Cangialosi