[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 260241
TCDAT5

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.


FORECAST POSITIONS AND MAX WINDS

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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