[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 250841
TCDAT5

Hurricane Tammy Discussion Number  28
NWS National Hurricane Center Miami FL       AL202023
500 AM AST Wed Oct 25 2023

Satellite data indicate Tammy has strengthened this morning.
Proxy-vis and infrared imagery depict a ragged eye has developed
with deep convection wrapping around the center. There has been no
microwave imagery this morning, but earlier SSMI/S and GMI
images showed a tight inner core. The subjective Dvorak final-T
intensity estimates have increased this cycle with a T5.0 and T4.5
from SAB and TAFB, respectively. Given the improved satellite
imagery and using a blend of these estimates, the initial intensity
is raised to 85 kt for this advisory.

Although vertical wind shear is analyzed to have increased over
the hurricane, the system is strengthening beneath upper-level
divergence associated with a deep-layer trough over the western
Atlantic. Models suggest some additional strengthening is possible
over the next 12 hours or so, which is reflected in the NHC
intensity forecast. Tammy is then expected to merge with a cold
front, which is currently analyzed by TAFB and OPC just northwest of
the system. Tammy is expected to undergo an extratropical
transition, with this transition forecast to be complete within 24
hours. As this transition occurs Tammy's wind field will expand as
it becomes a hurricane-force extratropical cyclone. Global models
are in fairly good agreement that the cyclone will then weaken
throughout the remainder of the forecast 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 at an estimated motion of 45 degrees
at 9 knots, 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 later today, then move slowly
northwestward in 2-3 days within weaker steering currents. The
long-range forecast remains uncertain, with not much run-to-run
model consistency and ensemble solutions that move in opposite
directions. Given the uncertainty, there is little change from the
previous forecast at this time range, with the NHC forecast track
showing the cyclone slowing and meandering through the end of the
the period.


FORECAST POSITIONS AND MAX WINDS

INIT  25/0900Z 25.6N  60.2W   85 KT 100 MPH
 12H  25/1800Z 27.0N  59.4W   90 KT 105 MPH
 24H  26/0600Z 28.9N  59.3W   75 KT  85 MPH...POST-TROP/EXTRATROP
 36H  26/1800Z 30.0N  60.4W   65 KT  75 MPH...POST-TROP/EXTRATROP
 48H  27/0600Z 30.6N  61.6W   60 KT  70 MPH...POST-TROP/EXTRATROP
 60H  27/1800Z 31.0N  62.3W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  28/0600Z 31.3N  62.9W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  29/0600Z 31.2N  63.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  30/0600Z 31.0N  63.9W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Kelly
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