Tropical Storm Gaston Discussion Number  20
NWS National Hurricane Center Miami FL       AL082022
900 AM GMT Sun Sep 25 2022

Gaston continues to generate an area of deep convection near and to 
the north of the center, as the interaction with the upper-level 
trough mentioned in the previous advisory continues to provide a 
favorable environment.  The initial intensity remains 45 kt based 
on the earlier scatterometer data and a satellite intensity 
estimate of 45 kt from TAFB.

The global models suggest that the favorable trough interaction 
should end in the next 12 h or so, and after that time Gaston 
should experience strong northwesterly shear in a convergent 
upper-level environment.  This, combined with cool sea surface 
temperatures of 24-25C and a dry airmass should cause the 
convection to dissipate and Gaston to become post-tropical.  The 
new intensity forecast has minor adjustments from the previous 
forecast, with the most significant change being keep the system as 
a tropical cyclone at the 12 h point.

Gaston has moved a little to the right of the previous forecast 
with the initial motion 285/9.  A building low- to mid-level ridge 
to the north and northwest of the cyclone should cause it to turn 
westward later today and then west-southwestward, with that motion 
continuing until the system dissipates.  Since the last advisory, 
the track guidance has shifted southward in the 24-72 h period.  
So, the new forecast track is also shifted southward, with the new 
track just to the north of the consensus models.


Key Messages:

1. Tropical storm conditions over the western Azores should diminish
by midday as Gaston moves away from the islands.

2. Gaston is expected to produce heavy rainfall over the western and
central Azores through midday. This rainfall may result in
landslides and areas of flooding.


FORECAST POSITIONS AND MAX WINDS

INIT  25/0900Z 39.0N  34.5W   45 KT  50 MPH
12H  25/1800Z 39.0N  36.5W   40 KT  45 MPH
24H  26/0600Z 38.7N  38.4W   35 KT  40 MPH...POST-TROPICAL
36H  26/1800Z 38.1N  40.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
48H  27/0600Z 37.5N  42.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
60H  27/1800Z 36.8N  45.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
72H  28/0600Z 36.1N  48.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
96H  29/0600Z...DISSIPATED

$$
Forecaster Beven