####018003108####
WTNT45 KNHC 230237

TCDAT5

 

Hurricane Tammy Discussion Number  19

NWS National Hurricane Center Miami FL       AL202023

1100 PM AST Sun Oct 22 2023

 

Satellite images show that Tammy has not become better organized

over the past several hours.  In fact, the Central Dense Overcast

(CDO) has become more fragmented in appearance and the center

appears to be near the southern portion of the CDO.  There are

however a couple of prominent convective bands over the eastern

portion of the circulation.  Upper-level outflow is restricted over

the southern semicircle of the system, suggesting the influence of

southerly vertical wind shear.  SFMR-observed surface winds from a

NOAA Hurricane Hunter aircraft conducting a research mission into

Tammy support a current intensity of 70-75 kt, so the advisory

intensity estimate is unchanged.

 

A center position estimate from the aircraft indicates that the

motion remains northwestward, or 325/8 kt at this time.  The

cyclone should turn northward to northeastward over the next 72

hours or so while moving around the western side of a mid-level

subtropical high.  Later in the forecast period, Tammy should begin

to interact with a cyclonic circulation that cuts off from an

eastward-moving mid-latitude trough over the western Atlantic.  

This should cause the system to turn westward around the northern 

side of the larger circulation in 3-5 days.  There continues to be 

a fairly large spread in the track guidance in this time frame, 

however.



The dynamical guidance indicates that Tammy will be in an 

environment of significant south-southwesterly vertical wind shear 

for the next few days.  This negative influence could be 

counteracted somewhat by the presence of a moist and unstable 

air mass along with warm ocean waters.  Therefore some slight 

strengthening is still predicted, along the lines of the 

Decay-SHIPS model.  This is also similar to the previous official 

intensity forecast.  By day 4, Tammy should begin to merge with a 

baroclinic zone and simulated satellite imagery from the GFS and 

ECMWF models depict a frontal appearance.  Therefore the system is 

forecast to have become extratropical by 96 hours.

  

 

KEY MESSAGES:

 

1.  Heavy rain from Tammy will remain possible over the British

Virgin Islands, Leeward Islands, and northern Windward Islands into

Monday morning.  This rainfall may produce isolated flash and urban

flooding, along with isolated mudslides in areas of higher terrain.

 

 

FORECAST POSITIONS AND MAX WINDS

 

INIT  23/0300Z 20.8N  64.0W   75 KT  85 MPH

 12H  23/1200Z 21.5N  63.9W   75 KT  85 MPH

 24H  24/0000Z 22.5N  63.4W   80 KT  90 MPH

 36H  24/1200Z 23.2N  62.6W   80 KT  90 MPH

 48H  25/0000Z 24.0N  61.6W   80 KT  90 MPH

 60H  25/1200Z 25.3N  60.4W   80 KT  90 MPH

 72H  26/0000Z 26.6N  59.5W   75 KT  85 MPH

 96H  27/0000Z 29.6N  60.5W   60 KT  70 MPH...POST-TROP/EXTRATROP

120H  28/0000Z 30.5N  64.5W   50 KT  60 MPH...POST-TROP/EXTRATROP

 

$$

Forecaster Pasch