Tropical Storm Gaston Forecast Discussion Number 12

By | September 23, 2022

360 
WTNT43 KNHC 230853
TCDAT3

Tropical Storm Gaston Discussion Number  12
NWS National Hurricane Center Miami FL       AL082022
900 AM GMT Fri Sep 23 2022

Gaston's cloud pattern has changed considerably in appearance 
since yesterday.  A tropical cyclone axisymmetric wind 
field that is typically concentrated about the surface center has 
transformed to a more asymmetric pattern with considerable 
expansion to the northeast due to the brisk mid-latitude 
westerlies and the sub-25C cool oceanic surface temperatures.  
Involvement between Gaston and a major shortwave trough/baroclinic 
zone noted in water vapor imagery and a recent AMSR2 microwave pass 
has resulted in a delta rain shield north of the exposed surface 
circulation.  A subsequent polar jet finger is visible in imagery 
northeast of the center, with possible warm seclusion development.  
All these attributes may well be leading to post-tropical cyclone 
transition.  The subjective satellite intensity estimates and a 
recent UW-CIMSS SATCON analysis yield an initial intensity of 50 kt 
for this advisory.  Gaston is forecast to slowly weaken while the 
cyclone completes its post-tropical transition in about 36 hours or 
so.  The official intensity forecast is similar to the previous one 
and is in line with the IVCN intensity consensus model.

Gaston has begun its anticyclonic loop and is moving 
east-southeastward, or 115/8 kt.  The cyclone is expected to turn 
toward the southeast today and southward along the southern 
periphery of mid-tropospheric ridge building to the north through 
Saturday morning while moving near the westernmost Azores.  
Afterward, Gaston should generally move toward the west-southwest 
and westward through the end of the period.  The official forecast 
is nudged slightly to the north of the previous one in the short 
term, but closer after that, and is based on the various consensus 
aids.


Key Messages:

1. Tropical storm conditions are occurring over portions of the
western Azores, and will likely spread to the central Azores later
today.

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


FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 40.5N  29.6W   50 KT  60 MPH
 12H  23/1800Z 39.7N  28.9W   50 KT  60 MPH
 24H  24/0600Z 38.6N  29.4W   50 KT  60 MPH
 36H  24/1800Z 38.2N  31.2W   50 KT  60 MPH...POST-TROPICAL
 48H  25/0600Z 38.6N  33.7W   50 KT  60 MPH...POST-TROPICAL
 60H  25/1800Z 38.6N  36.1W   45 KT  50 MPH...POST-TROPICAL
 72H  26/0600Z 38.6N  38.0W   40 KT  45 MPH...POST-TROPICAL
 96H  27/0600Z 39.1N  41.0W   35 KT  40 MPH...POST-TROPICAL
120H  28/0600Z 38.2N  45.3W   30 KT  35 MPH...POST-TROPICAL

$$
Forecaster Roberts


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