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Hurricane HILARY


Hurricane Hilary Discussion Number  18
NWS National Hurricane Center Miami FL       EP092017
300 PM MDT Tue Jul 25 2017

Hilary continues to have a somewhat asymmetric presentation on the
latest satellite imagery, with an eye feature in the northwestern
portion of the central dense overcast, suggestive of some
northwesterly shear.  The initial wind speed remains 90 kt since
there have been no significant changes to the satellite estimates.
Higher wind shear is not far away from the hurricane, as evidenced
by southward-moving cirrus clouds moving toward the center in the
northern semicircle. Thus the window of time for Hilary to intensify
may be closing, and little change in wind speed is shown for the
next day or so. Afterward, gradually cooling SSTs, entrainment of
drier air, and interaction with Hurricane Irwin is likely to cause
more significant weakening.  The NHC forecast is reduced from the
previous one in the near term due to the shear, and at long range as
Hilary probably moves over cold waters.  This is not a particularly
confident forecast at days 4-5 due to the interaction with Irwin.

The initial motion estimate is the same as previous, 285/10 kt. A
mid-tropospheric ridge extending westward from the southwestern
United States should cause Hilary to continue on a west to
west-northwestward track for the next several days.  In a few days,
however, Hilary is likely to pass close to Hurricane Irwin.  While
Irwin won't affect Hilary too much, the bulk of the guidance is
showing Hilary slowing down and turning slightly left as Irwin pulls
on Hilary's circulation.  Model guidance has become more divergent
after day 3, with the GFS indicating a northwestward motion due to
the ridge weakening along 120-125W.  The other guidance has been
more consistent, so only small changes were made to the latest NHC
forecast, which remains generally south and west of the model


INIT  25/2100Z 15.5N 108.8W   90 KT 105 MPH
 12H  26/0600Z 15.9N 110.5W   95 KT 110 MPH
 24H  26/1800Z 16.4N 112.7W   95 KT 110 MPH
 36H  27/0600Z 16.9N 114.8W   90 KT 105 MPH
 48H  27/1800Z 17.5N 116.8W   85 KT 100 MPH
 72H  28/1800Z 18.7N 120.4W   80 KT  90 MPH
 96H  29/1800Z 19.7N 124.0W   70 KT  80 MPH
120H  30/1800Z 20.5N 127.5W   50 KT  60 MPH

Forecaster Blake