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Tropical Storm GASTON Forecast Discussion

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WTNT42 KNHC 260245

1100 PM AST THU AUG 25 2016

Gaston continues to have an asymmetric satellite appearance due to
strong southwesterly shear.  Still, the cyclone is producing
persistent deep convection near the center, and Dvorak estimates
suggest the initial wind speed remains near 55 kt.  The shear
should decrease tomorrow due to Gaston moving into a favorable
position to the north of an upper-level low.  In addition, the
water temperatures are forecast to be warming up during the next
few days, which should also promote strengthening.  Due to recent
microwave data showing that the inner core has been disrupted, only
a slow intensification is shown in this forecast.  In the longer
term, models are not in great agreement on the upper-level wind
pattern, and I have elected to level off the intensification.  The
new NHC prediction is a blend of the previous one and the model
consensus. It should be noted that, while not explicitly shown
below, a majority of the guidance show Gaston becoming a major
hurricane at some time in the day 3 to 5 period.

The initial motion remains northwestward at 15 kt.  Gaston should
move northwestward during the next day or so around a mid-level
ridge over the east-central Atlantic.  In about 36 hours, the
ridge is forecast to build to the north of Gaston, which will likely
cause the cyclone to turn west-northwestward.  Early next week,
Gaston should turn northward as the ridge weakens, then recurve into
the mid-latitude westerlies in 4 days or so.  Model guidance,
however, is not in good agreement on the exact details, with timing
and speed differences in both the tropical cyclone's position and
the potential mid-latitude shortwave that causes recurvature.  Since
there have been no substantive changes to the model guidance in this
cycle, the new NHC prediction is basically just an update of the
previous one.  It is fair to say that the end of this forecast is
of pretty low confidence.


INIT  26/0300Z 22.8N  46.4W   55 KT  65 MPH
 12H  26/1200Z 24.5N  48.1W   55 KT  65 MPH
 24H  27/0000Z 26.2N  50.7W   60 KT  70 MPH
 36H  27/1200Z 27.5N  53.1W   65 KT  75 MPH
 48H  28/0000Z 28.6N  54.9W   75 KT  85 MPH
 72H  29/0000Z 30.5N  57.0W   90 KT 105 MPH
 96H  30/0000Z 32.5N  57.0W   95 KT 110 MPH
120H  31/0000Z 34.5N  53.0W   95 KT 110 MPH

Forecaster Blake