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Hurricane GERT


Hurricane Gert Discussion Number  15
NWS National Hurricane Center Miami FL       AL082017
1100 AM AST Wed Aug 16 2017

GOES-16 1-minute visible imagery has shown Gert's eye coming and
going over the past several hours, and for the first time a
distinct warm spot has appeared in infrared images.  However,
subjective Dvorak estimates are unchanged from six hours ago, and
the objective ADT has actually decreased a bit.  The initial
intensity is therefore held at 80 kt.  Gert has another 18-24 hours
before it reaches significantly colder waters north of the Gulf
Stream, so the cyclone still has the opportunity for a little more
strengthening later today and this evening.  Southwesterly shear is
expected to begin increasing tonight, and the higher shear and
colder water should cause a steady weakening trend to begin on
Thursday.  The global model fields indicate that Gert should be
fully extratropical, embedded in a frontal zone, within 48 hours,
and that is reflected in the official forecast.  There is still a
lot of uncertainty regarding when Gert will be absorbed by another
larger extratropical cyclone, but most of the guidance tends to
agree that it should be absorbed by day 5 over the north Atlantic.

Gert's forward speed continues to increase, and the hurricane is
now moving toward the northeast with a motion of 055/22 kt.  Gert
is embedded in mid-latitude westerly flow between a mid-level high
centered east of Bermuda and a large cut-off low over eastern
Canada, and this pattern should force the cyclone on a fast
northeastward pace over the north Atlantic at least for the next 72
hours.  A slower motion is forecast by day 4 once post-tropical
Gert interacts with the large cut-off low moving east of Atlantic
Canada.  There was very little change in the latest track guidance,
and no significant deviations from the previous NHC forecast were
required on this cycle.  The post-tropical portion of the track,
intensity, and wind radii forecasts incorporate guidance from NOAA's
Ocean Prediction Center.

Swells from Gert are affecting 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 day or two.  These
swells are likely to produce dangerous surf and rip current
conditions. Please consult products from your local weather forecast
office for more information.


INIT  16/1500Z 37.4N  65.7W   80 KT  90 MPH
 12H  17/0000Z 39.0N  61.3W   85 KT 100 MPH
 24H  17/1200Z 41.8N  53.6W   75 KT  85 MPH
 36H  18/0000Z 45.5N  45.2W   65 KT  75 MPH
 48H  18/1200Z 49.5N  38.4W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  19/1200Z 55.0N  32.2W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  20/1200Z 55.0N  26.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

Forecaster Berg