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Tropical Storm GASTON Forecast Discussion


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000
WTNT42 KNHC 270853
TCDAT2

TROPICAL STORM GASTON DISCUSSION NUMBER  19
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072016
500 AM AST SAT AUG 27 2016

Recent microwave data indicate that Gaston's center is now well
embedded near the middle of the central dense overcast.  The
microwave images also show that a partial mid-level ring has formed,
but it remains open to the north-northeast.  Even though Gaston's
structure appears to be improving, the maximum winds remain 55 kt
based on Dvorak Current Intensity numbers from TAFB and SAB.

Two outflow jets are emanating away to the east and southwest of
Gaston, but the outflow remains restricted to the south and
northwest.  Still, the shear has decreased substantially from what
it was a day or two ago, and it should remain generally low for the
next 48 hours.  In addition, sea surface temperatures ahead of
Gaston are expected to be at least 28C for several more days.
Therefore, strengthening is anticipated through day 3, followed by
gradual weakening on days 4 and 5 due to increasing westerly shear.
Although the intensity models all agree on this general scenario,
there is a little more spread in the peak intensities than has been
noted in previous advisories.  On the high end, the Florida State
Superensemble still shows Gaston approaching major hurricane
intensity, while the LGEM model is at the other extreme being about
20 kt lower.  The updated NHC intensity forecast is near the middle
of the guidance and ends up just a little lower than the previous
forecast.

Gaston is moving northwestward, or 310 degrees at 13 kt, between a
mid-tropospheric high to its northeast and a mid-/upper-level low
to its southwest.  The cyclone is expected to maintain a
northwestward heading but steadily decelerate during the next 48
hours.  After that time, Gaston should recurve sharply
east-northeastward and accelerate through the end of the forecast
period as it gets picked up by the mid-latitude westerlies.  The
track guidance has trended westward through 48 hours, delaying
Gaston's recurvature just a bit, and it is then a little faster by
days 4 and 5.  The NHC track forecast has been adjusted accordingly
and is close to the TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  27/0900Z 27.9N  52.0W   55 KT  65 MPH
 12H  27/1800Z 28.8N  53.6W   60 KT  70 MPH
 24H  28/0600Z 29.9N  55.0W   70 KT  80 MPH
 36H  28/1800Z 30.6N  56.0W   80 KT  90 MPH
 48H  29/0600Z 31.2N  56.8W   85 KT 100 MPH
 72H  30/0600Z 32.5N  55.6W   90 KT 105 MPH
 96H  31/0600Z 34.5N  50.5W   85 KT 100 MPH
120H  01/0600Z 37.0N  43.5W   75 KT  85 MPH

$$
Forecaster Berg