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Tropical Storm GASTON Forecast Discussion


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000
WTNT42 KNHC 260851
TCDAT2

TROPICAL STORM GASTON DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016
500 AM AST FRI AUG 26 2016

Gaston is right in the thick of 20-25 kt of southwesterly shear,
and the low-level center appears to be near or just inside the
southern edge of a ragged central dense overcast.  Because Dvorak
Current Intensity estimates from TAFB and SAB remain 3.5, the
initial intensity is held at 55 kt.  With Gaston now moving around
the northeastern side of a mid- to upper-level low, the vertical
shear is expected to quickly decrease to below 10 kt within the next
12-24 hours.  In addition, sea surface temperatures are forecast to
increase by another degree or two.  Therefore, Gaston is likely to
begin strengthening later today, and it should reintensify to a
hurricane by tonight or on Saturday.  Strengthening is anticipated
to continue through days 3 and 4, with Gaston nearing or possibly
reaching major hurricane intensity, followed by some weakening on
day 5 due to an increase in westerly shear.  The reliable intensity
models are all within 10-15 kt of each other for the entire
forecast period, and the NHC forecast is therefore very close to
the ICON intensity consensus.

Gaston continues to move northwestward, or 320 degrees at 15 kt.
The cyclone is expected to maintain a generally northwestward track
but slow down considerably during the next few days after it moves
north of the aforementioned mid- to upper-level low and enters a
break in the subtropical ridge.  After 72 hours, Gaston is expected
to reach the mid-latitude westerlies, and a sharp recurvature with
acceleration is forecast at the end of the forecast period.  While
all the track models agree on this scenario, there continue to be
differences in the sharpness of Gaston's turn and its forward speed,
especially after the turn.  Still, the updated NHC track forecast
is not too different from the previous one, and it is closest to a
clustering of models that includes the GFS, the Florida State
Superensemble, and the TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  26/0900Z 23.9N  47.6W   55 KT  65 MPH
 12H  26/1800Z 25.5N  49.5W   60 KT  70 MPH
 24H  27/0600Z 27.0N  52.1W   65 KT  75 MPH
 36H  27/1800Z 28.2N  54.2W   70 KT  80 MPH
 48H  28/0600Z 29.2N  55.7W   85 KT 100 MPH
 72H  29/0600Z 30.8N  57.1W   95 KT 110 MPH
 96H  30/0600Z 32.2N  55.8W   95 KT 110 MPH
120H  31/0600Z 34.0N  51.5W   90 KT 105 MPH

$$
Forecaster Berg