Official Discussion issued by the National Hurricane Center

Tammy (AL202023) DATA RELEASED: 10/25/2023 9:00:00 AM UTC

Copy of official data

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.


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