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TROPICAL STORM GASTON DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016
1100 PM AST FRI AUG 26 2016

The structure of Gaston appears to be slowly improving, with less
evidence of vertical shear than earlier today.  Deep convection has
been forming fairly close to the center in a more symmetric fashion,
but still hasn't been able to persist for very long.  Subjective
estimates are a little higher than earlier, but still support an
initial wind speed of 55 kt for this advisory.

Gaston should move into a low-shear, warm-water environment during
the next 2 or 3 days, which would usually support a great deal of
strengthening.  However, a key hindering factor remains the nearby
low-level moisture, which is forecast to substantially decrease
during the next few days.  This should temper the expected
intensification and reduce the chances for rapid strengthening.
Gaston is likely to encounter increasing upper-level flow beyond 3
days, which probably will start a weakening trend in combination
with gradually cooling SSTs.  Model guidance is generally in good
agreement on this scenario, with less spread in the intensity
models than is typically seen.  The new prediction is a blend of
the previous forecast and the intensity consensus.

Microwave data suggest that Gaston continues to move northwestward,
now at about 13 kt, a bit slower than before.  The cyclone is
moving between a strong upper low to the southwest and a subtropical
ridge to its northeast.  The ridge is forecast to gradually weaken,
resulting in Gaston decelerating over the next couple of days.
Steering currents get quite light in about 3 days, and the cyclone
is expected to turn northeastward or east-northeastward it moves
around the northwest side of a distant ridge over the eastern
Atlantic.   Computer models are coming into better agreement on a
sharper, slower recurvature, first suggested by the ECMWF yesterday.
The latest NHC forecast is close to the previous one for the first
few days, then is trended eastward to follow the model trend.


FORECAST POSITIONS AND MAX WINDS

INIT  27/0300Z 27.0N  50.8W   55 KT  65 MPH
 12H  27/1200Z 28.0N  52.5W   60 KT  70 MPH
 24H  28/0000Z 29.2N  54.1W   70 KT  80 MPH
 36H  28/1200Z 30.2N  55.2W   80 KT  90 MPH
 48H  29/0000Z 30.8N  55.7W   90 KT 105 MPH
 72H  30/0000Z 31.8N  55.4W   95 KT 110 MPH
 96H  31/0000Z 33.0N  52.0W   90 KT 105 MPH
120H  01/0000Z 35.0N  47.5W   80 KT  90 MPH

$$
Forecaster Blake

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