000
WTNT44 KNHC 182036
TCDAT4

Tropical Storm Harvey Discussion Number   6
NWS National Hurricane Center Miami FL       AL092017
500 PM AST Fri Aug 18 2017

Again, there has been little change in the structure of Harvey,
with the low-level center near the eastern edge of a strong, but
poorly organized, convective area.  Earlier reports from an Air
Force Reserve Hurricane Hunter aircraft included winds suggesting
an increased intensity.  However, due to uncertainties in how
representative these measurements were, no appreciable change in
the central pressure, and no improvement in the structure, the
initial intensity is held at 35 kt.

The initial motion is 275/18.  A strong low- to mid-level ridge
north of the cyclone should keep Harvey on this general motion
for the next 3 days or so, with the system moving from the eastern
to the western Caribbean Sea during this time.  After 72 h, a
west-northwestward motion with a decrease in forward speed is
expected when Harvey passes near or over portions of Central
America, the Yucatan Peninsula, and eastern Mexico.  The new
forecast track is a little faster then the previous track, but
there were only minor changes in the direction.  It should be noted
that there is considerable uncertainty about how far north Harvey
might get over the Bay of Campeche, with several of the large-scale
models not bringing the center back over the water on the latest
runs.

The current shear should persist for about the next 48 h, and
thus the intensity forecast continues the trend of slow
strengthening during this time.  However, the GFS and ECMWF again
forecast Harvey to degenerate to an open wave during this time, and
the rest of the intensity guidance has trended toward a weaker
cyclone.  This lowers the confidence in intensification.  After
48 h, conditions appear more favorable for strengthening, with the
main uncertainty being how much land Harvey will encounter.  The
intensity forecast will again call for a peak intensity of 60 kt in
72 h, followed by weakening due to land interaction.


FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 13.4N  62.9W   35 KT  40 MPH
 12H  19/0600Z 13.6N  65.7W   35 KT  40 MPH
 24H  19/1800Z 13.9N  69.3W   40 KT  45 MPH
 36H  20/0600Z 14.2N  73.0W   40 KT  45 MPH
 48H  20/1800Z 14.5N  76.7W   45 KT  50 MPH
 72H  21/1800Z 15.5N  83.5W   60 KT  70 MPH
 96H  22/1800Z 17.5N  88.5W   50 KT  60 MPH...INLAND
120H  23/1800Z 19.0N  92.0W   30 KT  35 MPH...OVER WATER

$$
Forecaster Beven