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WTNT45 KNHC 250239

TCDAT5

 

Hurricane Tammy Discussion Number  27

NWS National Hurricane Center Miami FL       AL202023

1100 PM AST Tue Oct 24 2023

 

Satellite data indicate Tammy has strengthened tonight. Deep 

convection has increased near and over the center of the hurricane 

during the past several hours, resulting in a cold and expanding 

central dense overcast with intermittent glimpses of a ragged eye. 

Recent SSMIS and GMI passive microwave images show a tighter inner 

core compared to earlier today, with a mid-level eyewall that mostly 

wraps around the center. The subjective Dvorak estimates from SAB 

and TAFB have risen to T4.5/77 kt and T4.0/65 kt, respectively, with 

similar increases in the various UW-CIMSS objective estimates. Thus, 

the initial intensity is raised to 75 kt for this advisory.

 

Despite strengthening upper-level winds over Tammy, increasing 

upper-level divergence associated with a deep-layer trough over the 

western Atlantic could support some additional intensification in 

the near term, as shown by the GFS and some of the regional models. 

Given recent trends, the updated NHC intensity forecast is raised at 

12-24 h to account for this potential. Then, Tammy is expected to 

merge with a cold front currently analyzed to the northwest of the 

hurricane. This extratropical transition is forecast to be completed 

by 36 h, with an expansion of Tammy's wind field as it becomes a 

hurricane-force extratropical cyclone. Thereafter, the global models 

show the frontal cyclone weakening through the rest of the period. 

There is some potential it could shed its frontal structure this 

weekend, but for now the model-simulated satellite imagery does not 

show much increase in convection during that time. 



Tammy is moving northeastward (50 degrees/8 kt) within the flow 

between a deep-layer trough over the western Atlantic and a 

subtropical ridge over the central Atlantic. Tammy is expected to 

turn northward during the next day or so as it becomes captured by 

the upper trough. The updated NHC forecast lies slightly right of 

the previous one in the first 24 h, mostly based on the more 

northeastward initial position. Then, the cyclone is forecast to 

move more slowly northwestward in 2-3 days within weaker steering 

currents. The long-range track forecast is highly uncertain, with 

diverging global and ensemble model solutions that move the 

shallower cyclone in opposite directions. Given the above-average 

uncertainty, it seems prudent to make little change to this portion 

of the track forecast at this time.

 

 

FORECAST POSITIONS AND MAX WINDS

 

INIT  25/0300Z 24.9N  60.7W   75 KT  85 MPH

 12H  25/1200Z 26.1N  59.9W   85 KT 100 MPH

 24H  26/0000Z 28.1N  59.1W   80 KT  90 MPH

 36H  26/1200Z 29.6N  59.7W   70 KT  80 MPH...POST-TROP/EXTRATROP

 48H  27/0000Z 30.5N  60.9W   60 KT  70 MPH...POST-TROP/EXTRATROP

 60H  27/1200Z 30.9N  61.8W   55 KT  65 MPH...POST-TROP/EXTRATROP

 72H  28/0000Z 31.3N  62.7W   50 KT  60 MPH...POST-TROP/EXTRATROP

 96H  29/0000Z 31.4N  63.6W   45 KT  50 MPH...POST-TROP/EXTRATROP

120H  30/0000Z 31.0N  64.5W   40 KT  45 MPH...POST-TROP/EXTRATROP

 

$$

Forecaster Reinhart