[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 240844
TCDAT3

Tropical Storm Gaston Discussion Number  16
NWS National Hurricane Center Miami FL       AL082022
900 AM GMT Sat Sep 24 2022

Since yesterday, Gaston has been transitioning to an asymmetric
warm core post-tropical cyclone.  A Friday morning 1227Z METOP-C
scatterometer data confirmed that the transition had begun by
depicting growing asymmetry in the wind field with a hundred-mile
increase in gale-force winds in the northwest quadrant.  Subsequent
surface winds less than 60 miles from the center were 20 kt or
less, all characteristics of a post-tropical/extratropical cyclone
wind profile.  The initial intensity is set at a generous 45 kt and
is above the various subjective and objective satellite intensity
estimates.

As a result of increasing deep-layer shear and decreasing sea
surface temperature beneath the cyclone, Gaston's organized deep
convection has diminished considerably.  Only a few convective
fragments remain well displaced to the southeast of the surface
center.  Accordingly, further weakening is expected, and Gaston
should complete its post-tropical transition later today.  A couple
of the global models, however, indicate a mid-latitude shortwave
trough/baroclinic zone interacting with post-tropical Gaston early
Sunday morning, which could create a flare-up of deep convection,
but this should be a short-lived event.

Gaston's initial motion is estimated to be west-southwestward, or
250/8 kt.  Building high pressure over the northeast Atlantic
should continue to steer the post-tropical cyclone westward through
Monday morning, and west-southwestward until dissipation occurs
toward the end of the week.  The official track forecast is a
little faster than the previous advisory and is nudged to the
south beyond 48 hours to agree more with the NOAA HFIP HCCA model.


Key Messages:

1. Tropical storm conditions over the western and central Azores
today should diminish this evening as Gaston moves away from the
islands.

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


FORECAST POSITIONS AND MAX WINDS

INIT  24/0900Z 38.6N  30.2W   45 KT  50 MPH
 12H  24/1800Z 38.3N  31.5W   45 KT  50 MPH...POST-TROPICAL
 24H  25/0600Z 38.7N  34.0W   40 KT  45 MPH...POST-TROPICAL
 36H  25/1800Z 38.7N  36.4W   35 KT  40 MPH...POST-TROPICAL
 48H  26/0600Z 38.1N  38.2W   35 KT  40 MPH...POST-TROPICAL
 60H  26/1800Z 37.4N  39.9W   35 KT  40 MPH...POST-TROPICAL
 72H  27/0600Z 36.6N  41.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  28/0600Z 33.9N  47.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  29/0600Z...DISSIPATED

$$
Forecaster Roberts
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