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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
 
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