Official Discussion issued by the National Hurricane Center

(AL202023) DATA RELEASED: 10/26/2023 9:00:00 AM UTC

Copy of official data

Post-Tropical Cyclone Tammy Discussion Number  32
NWS National Hurricane Center Miami FL       AL202023
500 AM AST Thu Oct 26 2023

Tammy appears to have completed its transition to a post-tropical 
cyclone, merging with the nearby front. The cloud pattern has become 
more comma shaped, with a long linear convective band, and  is no 
longer producing deep convection near the center. The cyclone is 
now frontal but likely still has a warm core, indicating that it is 
a warm seclusion-type of extratropical cyclone. Despite the 
transition, it remains a strong cyclone, and the initial intensity 
is 75 kt, based on current intensity satellite estimates. 

The cyclone has slowed down and made a northward turn overnight, and 
recently the system is turning more north-northwestward. The 
estimated long-term motion is 355/10 kt. Over the next day or so, 
Tammy is forecast to slow down and move generally northwestward to 
west-northwestward. Beyond 36 h there continues to be high 
uncertainty in the track forecast, with no more clarity from the 
latest global model runs. The global models continue to have 
enormous spread, and ensemble solutions that diverge in opposite 
directions. Given the uncertainty, there is little change from the 
previous forecast at this time range.

Although post-tropical, Tammy remains a powerful cyclone. In the 
near term, the increasing shear and drier air associated with a 
deep-layer trough to the west should continue to cause convection to 
dissipate, and the system to weaken over the next few days. Global 
model fields indicate Tammy could shed its frontal structure by 36 
h. A reduction in wind shear is forecast soon thereafter, and 
convection could redevelop near Tammy's center in about 2-3 days 
while it moves over 25-26C sea surface temperatures. Though it is 
not explicitly forecast, there is some potential based on the GFS 
and ECMWF simulated satellite imagery that Tammy could reacquire 
tropical characteristics this weekend or early next week. The 
chances of the system transitioning back to a tropical cyclone will 
be evaluated in routine Tropical Weather Outlooks.

This is the last NHC advisory. Additional information on this system 
can be found in High Seas Forecasts issued by the National Weather 
Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and 
online at


INIT  26/0900Z 30.5N  58.4W   75 KT  85 MPH...POST-TROP/EXTRATROP
12H  26/1800Z 31.2N  59.6W   65 KT  75 MPH...POST-TROP/EXTRATROP
24H  27/0600Z 31.5N  61.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
36H  27/1800Z 31.9N  62.2W   55 KT  65 MPH...POST-TROPICAL
48H  28/0600Z 32.3N  62.1W   50 KT  60 MPH...POST-TROPICAL
60H  28/1800Z 32.4N  61.2W   50 KT  60 MPH...POST-TROPICAL
72H  29/0600Z 32.4N  60.4W   45 KT  50 MPH...POST-TROPICAL
96H  30/0600Z 32.3N  59.6W   40 KT  45 MPH...POST-TROPICAL
120H  31/0600Z 32.2N  58.4W   35 KT  40 MPH...POST-TROPICAL

Forecaster Kelly