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Hurricane Gert Discussion Number  14
NWS National Hurricane Center Miami FL       AL082017
500 AM AST Wed Aug 16 2017

Gert has strengthened a little more during the last several hours.
There have been some hints of an eye in infrared satellite images
overnight, and the center is embedded beneath a large area of cold
cloud tops.  The latest Dvorak classifications are both 4.5/77 kt
from TAFB and SAB, and recent ADT values are a little higher.  Based
on these estimates, the initial wind speed is nudged upward to 80
kt.  The hurricane is forecast to strengthen a little more during
the next 12 to 24 hours while it remains over the warm waters of the
Gulf Stream and in a favorable upper-level wind pattern.  After that
time, sharply colder waters, a significant increase in west-
southwesterly shear, and drier air should end the strengthening
trend and cause weakening.  The models are in good agreement in
showing Gert losing its tropical characteristics in 36 to 48 hours.
The NHC intensity forecast is largely an update of the previous one.

Gert continues to pick up speed, and it is now moving northeastward
at 18 kt.  The hurricane is located between a subtropical ridge to
its southeast and a large deep-layer low pressure system to its
northwest.  Gert is expected to turn to the east-northeastward and
accelerate some more during the next couple of days while it becomes
embedded in the fast mid-latitude flow.  Beyond a couple of days,
when Gert is post-tropical, the system is forecast to slow down and
move more erratically while it interacts and ultimately merges with
another extratropical low.  The NHC track forecast lies closest to
the various consensus aids.  The post-tropical portion of the
track, intensity, and wind radii forecasts are based on guidance
provided by NOAA's Ocean Prediction Center.

Swells from Gert are beginning to reach portions of the
mid-Atlantic coast of the United States, and are expected to spread
northward to New England and Atlantic Canada during the next couple
of days.  These swells are likely to produce dangerous surf and rip
current conditions.  Please consult products from your local weather
forecast office for more information.

FORECAST POSITIONS AND MAX WINDS

INIT  16/0900Z 36.0N  68.4W   80 KT  90 MPH
 12H  16/1800Z 37.7N  64.8W   85 KT 100 MPH
 24H  17/0600Z 40.0N  58.2W   85 KT 100 MPH
 36H  17/1800Z 43.2N  50.1W   75 KT  85 MPH
 48H  18/0600Z 47.0N  42.6W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  19/0600Z 54.0N  33.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  20/0600Z 55.5N  27.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  21/0600Z 57.5N  12.0W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi

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