[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 210257
TCDAT3

Tropical Storm Gaston Discussion Number   3
NWS National Hurricane Center Miami FL       AL082022
300 AM GMT Wed Sep 21 2022

The satellite presentation of Gaston has improved slightly since
the previous advisory, with deep convection persisting over the
low-level circulation center. The latest current intensity
estimates reflect what has been seen in the satellite imagery, with
TAFB and SAB coming in at 45 knots, while the ADT and AiDT values
from UW-CIMSS showing 35 knots and 46 knots respectively. Based on
a blend of these data along with the improved satellite appearance,
the initial intensity has been raised to 45 knots.

Gaston continues on a path toward the north-northeast,
with the initial motion estimated to be 020/16 kt.  A turn to
northeast is expected today, followed by a turn to the east by
Thursday as the tropical storm moves along the the northern
periphery of a subtropical ridge. By late this week, Gaston is
expected to stall to the west of the Azores in weak steering
currents as a mid-level ridge builds to the north of cyclone. 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, and closely follows the consensus track guidance.

The period for additional intensification is quickly closing, as
Gaston is moving over the 26C isotherm, and will move over
progressively cooler water through the remainder of the forecast
period. Additionally, the impact of the vertical wind shear will
increase in a couple days as the tropical cyclone stalls out while
westerly shear holds in the 25 to 30 knot range. As a result, the
intensity forecast calls for slight strengthening today, followed by
little change in strength for another day or so after that. The
combination of cool SSTs, dry mid-level air, and increasing vertical
wind shear should then lead to slow weakening through the remainder
of the week. The latest NHC was adjusted upward through the first 24
hours to account for the strengthening which has already occurred,
with only minor adjustments made through the remainder of the
forecast period, closely following the consensus intensity aids.

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


FORECAST POSITIONS AND MAX WINDS

INIT  21/0300Z 36.2N  43.6W   45 KT  50 MPH
 12H  21/1200Z 37.8N  41.9W   50 KT  60 MPH
 24H  22/0000Z 39.3N  39.1W   50 KT  60 MPH
 36H  22/1200Z 40.2N  36.0W   50 KT  60 MPH
 48H  23/0000Z 40.4N  32.9W   45 KT  50 MPH
 60H  23/1200Z 40.4N  31.9W   45 KT  50 MPH
 72H  24/0000Z 40.4N  31.9W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  25/0000Z 41.5N  33.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  26/0000Z 43.5N  35.2W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster D. Zelinsky/Jelsema
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