[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 211437
TCDAT3

Tropical Storm Gaston Discussion Number   5
NWS National Hurricane Center Miami FL       AL082022
Issued by the NWS Weather Prediction Center College Park MD
300 PM GMT Wed Sep 21 2022

Satellite images indicate that Gaston continues to produce
convection that has become increasingly symmetric around the center.
In addition, there is a broken band of thunderstorms on the eastern
side of the system.  The Dvorak classifications from TAFB and SAB
were both 3.5/55 kt.  A recent ASCAT-B pass indicate that Gaston has
a relatively symmetric wind field with maximum winds in the 45-50 kt
range.  Based on this data, the initial intensity remains 55 kt for
this advisory.  It is worth mentioning that satellite data indicate
that Gaston is not purely tropical and is likely a hybrid system
gaining energy from baroclinic sources.

Gaston continues to track northeastward over the north-central
Atlantic, with the latest initial motion estimated to be 035/14 kt.
Although there is no significant change to the forecast reasoning,
there is a modest amount of model spread in the details of the
future steering pattern.  The NHC track is faster and a tad south of
the previous forecast, trending toward the latest consensus models.
Gaston is expected to turn to the east in a day or so when it moves
on the northern side of a subtropical ridge and then will likely
slow down considerably or completely stall near or just west of the
western Azores late this week.  If the storm survives, a turn to the
north or northwest could occur over the weekend.

The storm could strengthen a little today given recent trends in
its convective development near and around the center.  However,
weakening should begin on Thursday when Gaston moves over cooler
waters and into a region of drier air and slightly stronger
westerly vertical wind shear.  An approaching mid-level trough
should aid in the system's transition to an extratropical cyclone
in a couple of days or so.  The NHC intensity forecast lies near
the middle of the guidance envelope.

Interests in the Azores should continue to monitor the forecast for
Gaston.  For additional information, see warnings and products
issued by the meteorological service in the Azores.


FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 38.3N  41.3W   55 KT  65 MPH
 12H  22/0000Z 39.5N  39.0W   60 KT  70 MPH
 24H  22/1200Z 40.6N  35.6W   55 KT  65 MPH
 36H  23/0000Z 40.9N  32.6W   55 KT  65 MPH
 48H  23/1200Z 40.8N  30.7W   50 KT  60 MPH
 60H  24/0000Z 40.5N  30.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  24/1200Z 40.0N  30.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  25/1200Z 41.2N  34.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  26/1200Z 42.5N  36.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi/Kong/Gallina
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