[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 210856
TCDAT3

Tropical Storm Gaston Discussion Number   4
NWS National Hurricane Center Miami FL       AL082022
900 AM GMT Wed Sep 21 2022

Gaston has continued to improve on satellite imagery overnight.
Curved bands can be seen rotating fully around the southwestern
side
of the tropical cyclone with a warm spot occasionally apparent near
where the center is. I was somewhat skeptical that this structure
was indicative of a formative inner core, but a helpful GMI
microwave pass at 0407 UTC revealed this was no illusion, with a
nearly closed ring of convection on both 89 and 37 GHz channels.
Subjective Dvorak classifications from SAB were T3.0/45-kt and
TAFB T3.5/55-kt. Given the improvement in structure tonight, the
winds have been increased to 55-kt this advisory.

Gaston continues to move to the north-northeast at 025/16 kt. A
turn
north northeastward is expected later today followed by a more
eastward motion by Thursday. By the latter part of this week,
Gaston
is forecast to come to near screeching halt to the west of the
Azores in weak steering currents as a mid-level ridge builds
northward, related to Fiona's downstream diabatic induced ridging.
A
turn to the northwest or north is expected over the weekend as
Gaston moves in the steering flow between Hurricane Fiona to the
west and the building mid-level ridge to the east. The latest NHC
track forecast has changed little and lies very close to the
previous advisory track.

Based on the current structure, Gaston might be able to intensify a
bit more today. However as Gaston slows down the westerly
upper-level flow the storm is embedded will likely cause the
structure to deteriorate, with both the GFS and ECMWF simulated
satellite imagery suggesting the convection could de-couple from
the storm in about 48-60 hours. Thus, the latest forecast shows
weakening during this time period, and Gaston could become a
post-tropical extratropical cyclone as soon as 72 hours. The latest
NHC intensity forecast is a bit higher, owing to the initial
intensity, but remains fairly close to the previous forecast after
60 hours.

Interests in the Azores should continue to monitor the forecast for
Gaston.


FORECAST POSITIONS AND MAX WINDS

INIT  21/0900Z 37.5N  42.6W   55 KT  65 MPH
 12H  21/1800Z 38.8N  40.6W   60 KT  70 MPH
 24H  22/0600Z 40.1N  37.7W   60 KT  70 MPH
 36H  22/1800Z 40.8N  34.7W   55 KT  65 MPH
 48H  23/0600Z 40.9N  32.6W   50 KT  60 MPH
 60H  23/1800Z 40.8N  31.4W   45 KT  50 MPH
 72H  24/0600Z 41.3N  31.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  25/0600Z 42.6N  33.7W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  26/0600Z 44.3N  35.2W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin
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