[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

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
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