[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

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
This weather bulletin was brought to you by:
www.nashvilleweather.net