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Tropical Storm Harvey Discussion Number   5
NWS National Hurricane Center Miami FL       AL092017
1100 AM AST Fri Aug 18 2017

The structure of Harvey has changed little during the past several
hours, and overall the storm is poorly organized.  The low-level
center is near the eastern edge of the convective mass due
to the affects of 15 kt of vertical wind shear.  In addition,
surface observations and Air Force Reserve Hurricane Hunter data
suggest that the 850-mb center is located west or southwest of the
surface center.  Based on the aircraft and surface data, the central
pressure is near 1005 mb and the initial intensity remains 35 kt.

The initial motion is a quick 270/18.  A strong low- to mid-level
ridge north of the cyclone should keep Harvey on this general motion
for the next 3-4 days, with the system moving from the eastern to
the western Caribbean Sea during this time.  Late in the forecast
period, a more northerly motion is expected when Harvey passes near
or over portions of Central America, the Yucatan Peninsula, and
eastern Mexico.  The new forecast track remains in the center of the
guidance, and only minor changes were made to the previous track.

The current shear should persist for the next 48 h or so, and thus
the intensity forecast continues the trend of slow strengthening
during this time.  After that, conditions appear favorable for
strengthening, with the main uncertainty being how much land Harvey
will encounter.  The ECMWF keeps the cyclone a little north of
Nicaragua and Honduras and allows more room for development, while
the GFS forecasts landfall in northeastern Nicaragua and thus has a
weaker intensity.  The new NHC forecast is close to the previous
one in showing a peak intensity below hurricane strength, but
the confidence in this portion of the forecast is low.

FORECAST POSITIONS AND MAX WINDS

INIT  18/1500Z 13.1N  61.3W   35 KT  40 MPH
 12H  19/0000Z 13.3N  63.8W   35 KT  40 MPH
 24H  19/1200Z 13.6N  67.3W   40 KT  45 MPH
 36H  20/0000Z 14.0N  71.1W   40 KT  45 MPH
 48H  20/1200Z 14.3N  75.0W   50 KT  60 MPH
 72H  21/1200Z 15.0N  82.0W   60 KT  70 MPH
 96H  22/1200Z 16.5N  87.5W   55 KT  65 MPH
120H  23/1200Z 18.5N  91.0W   30 KT  35 MPH...INLAND

$$
Forecaster Beven

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