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Hurricane Gert Discussion Number  11
NWS National Hurricane Center Miami FL       AL082017
1100 AM EDT Tue Aug 15 2017

Northerly shear of about 20 kt was inhibiting Gert overnight.  A
pair of microwave passes around 0900 UTC showed that the mid-level
center was displaced about 20 n mi south-southeast of the
low-level center.  Since the time of the earlier microwave passes,
outflow in the northwest quadrant has become re-established,
suggesting that the shear may be lessening.  The initial intensity
has been held at 65 kt based on the latest Dvorak classification
from TAFB.  Environmental diagnostics from SHIPS indicate that the
shear should continue to decrease for about the next 24 h, which
should allow for a brief window of intensification.  The GFS, ECMWF,
and UKMET all indicate that extratropical transition will begin
sometime between 36 h and 48 h, while the hurricane crosses a strong
SST gradient and the shear increases above 30 kt.  Gert is forecast
to become fully extratropical about a day later.

The initial motion is 015/9 kt.  Gert has finally begun to round
the western edge of the subtropical ridge, and should begin
accelerating northeastward later today.  The track guidance is
tightly clustered for the first 48 h of the forecast.  Beyond two
days, there is some along-track spread in the models.  The GFS
forecasts that Gert will move faster and remain separated from a
large extratropical low for nearly 5 days, while the ECMWF and UKMET
forecast Gert to move slower, causing it to merge with the
extratropical low sooner.  The official forecast splits the
difference between these scenarios for now and indicates that Gert
will be absorbed by the extratropical low shortly after 96 h.

Swells from Gert are expected to spread northward along the
mid-Atlantic coast of the United States during the next few days.
These swells are likely to produce dangerous surf and rip current
conditions.  Please consult products from your local National
Weather Service office.


FORECAST POSITIONS AND MAX WINDS

INIT  15/1500Z 32.8N  72.0W   65 KT  75 MPH
 12H  16/0000Z 34.4N  70.7W   70 KT  80 MPH
 24H  16/1200Z 36.7N  67.0W   75 KT  85 MPH
 36H  17/0000Z 38.9N  61.2W   75 KT  85 MPH
 48H  17/1200Z 41.3N  53.3W   70 KT  80 MPH
 72H  18/1200Z 48.8N  38.3W   60 KT  70 MPH...POST-TROP/EXTRATROP
 96H  19/1200Z 54.0N  34.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  20/1200Z...DISSIPATED

$$
Forecaster Zelinsky

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