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Hurricane Tammy Discussion Number  22
NWS National Hurricane Center Miami FL       AL202023
500 PM AST Mon Oct 23 2023
 
Moderate southwesterly vertical wind shear seems to be disrupting
Tammy's circulation.  Deep convection is being pulled northward away
from the estimated low-level center and mid-level dry air is working
its way around the southern side of the cyclone.  Satellite
intensity estimate have decreased this cycle to 55 and 65 kt from
SAB and TAFB, respectively.  The initial intensity has therefore
been lowered to 65 kt.  While ASCAT missed the majority of the
hurricane's core, it did show winds on the western portion of the
circulation have decreased and the radii have been adjusted inward
accordingly.
 
Tammy is moving north-northeastward at 6 kt.  A turn toward the 
northeast is forecast shortly as Tammy is steered by a mid-level 
ridge centered over the central subtropical Atlantic and the flow 
ahead of a mid-latitude trough over the western Atlantic.  Between 
48-60 h, the model solutions begin to bifurcate.  The ECMWF turns 
the hurricane northward and then westward by the end of the forecast 
period.  The GFS and regional models tend to turn Tammy toward the 
north and northeastward by day 5.  The official forecast still 
favors the ECMWF forecast and is similar to the previous advisory.
 
Models suggest that environmental conditions will be relatively 
unfavorable.  The deep-layer vertical wind shear is forecast to 
increase and surrounding mid-level moisture to decrease through most 
of the forecast period.  However, in a day or so, when the hurricane 
begins to interacts with the trough to its west, upper-level 
divergence could enhance convection and cause some strengthening 
through about 48 h.  Tammy is then expected to gradually weaken and 
complete its transition into an extratropical cyclone by day 3.  The 
NHC intensity forecast is similar to the previous prediction, with a 
slightly lower peak intensity of 75 kt.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/2100Z 22.3N  63.6W   65 KT  75 MPH
 12H  24/0600Z 23.0N  62.9W   70 KT  80 MPH
 24H  24/1800Z 24.0N  61.7W   75 KT  85 MPH
 36H  25/0600Z 25.3N  60.3W   75 KT  85 MPH
 48H  25/1800Z 26.8N  59.0W   75 KT  85 MPH
 60H  26/0600Z 28.9N  58.6W   70 KT  80 MPH
 72H  26/1800Z 30.3N  59.3W   60 KT  70 MPH...POST-TROP/EXTRATROP
 96H  27/1800Z 31.7N  62.1W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  28/1800Z 32.5N  65.2W   45 KT  50 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Bucci
 
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