Hurricane Tammy Forecast Discussion Number 31

By | October 26, 2023

WTNT45 KNHC 260241

Hurricane Tammy Discussion Number  31
NWS National Hurricane Center Miami FL       AL202023
1100 PM AST Wed Oct 25 2023

The extratropical transition of Tammy appears to be well underway. 
The eye is no longer apparent in satellite images, and deep 
convection has eroded over the western portion of the circulation. A 
dry slot has become evident between the small area of convection 
near Tammy's center and a long, linear convective band well to its 
east and southeast. Based on the lower satellite intensity estimates 
this evening, the initial intensity is brought down to 80 kt for 
this advisory.

If it hasn't already, Tammy is expected to completely merge with a 
nearby front soon. In the near term, the increasing shear and drier 
air associated with a deep-layer trough to the west should result in 
a significant disruption of Tammy's convection. However, Tammy will 
remain a powerful cyclone even after it becomes post-tropical, with 
an expanding outer wind field during this time. After the rapid warm 
seclusion process is completed, 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 2-3 days while it moves over 25-26C waters. 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 long-term motion of Tammy is 015 degrees/17 kt, but more 
recently the cyclone appears to be turning northward as expected. 
Over the next day or so, Tammy is forecast to slow down and move 
generally northwestward. From there, the global and regional models 
offer little clarity regarding the future track of Tammy, with 
extremely divergent solutions beyond about 36 h. The track 
differences appear to be related to the extent of Tammy's 
interaction with a cutoff mid-level low that develops to the 
southwest of Tammy later this week. Several of the global models 
(ECMWF, UKMET, CMC) show this feature moving westward and remaining 
far enough away from Tammy that little interaction occurs. These 
models move Tammy generally eastward through early next week. The 
latest GFS and regional model runs show Tammy rotating around this 
mid-level feature and moving much farther west and southwest over 
the southwestern Atlantic. The spread between the 96-h GFS and ECMWF 
forecast positions is almost 1400 n mi, making the longer-term track 
forecast highly uncertain. Given this enormous spread, little change 
was made to the official forecast tonight.


INIT  26/0300Z 29.9N  57.8W   80 KT  90 MPH
 12H  26/1200Z 30.7N  58.6W   70 KT  80 MPH...POST-TROP/EXTRATROP
 24H  27/0000Z 31.3N  59.8W   60 KT  70 MPH...POST-TROP/EXTRATROP
 36H  27/1200Z 31.6N  60.8W   60 KT  70 MPH...POST-TROPICAL
 48H  28/0000Z 31.9N  62.0W   55 KT  65 MPH...POST-TROPICAL
 60H  28/1200Z 32.1N  61.7W   55 KT  65 MPH...POST-TROPICAL
 72H  29/0000Z 32.2N  61.0W   50 KT  60 MPH...POST-TROPICAL
 96H  30/0000Z 32.4N  60.1W   40 KT  45 MPH...POST-TROPICAL
120H  31/0000Z 32.5N  59.0W   35 KT  40 MPH...POST-TROPICAL

Forecaster Reinhart

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