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Hurricane Hilary Discussion Number  21
NWS National Hurricane Center Miami FL       EP092017
900 AM MDT Wed Jul 26 2017

Satellite images indicate that Hilary remains a powerful hurricane.
The central dense overcast has become more symmetric, although
convection is still preferentially forming in the eastern eyewall.
Any eye feature, however, is somewhat less distinct than a few hours
ago, and the latest microwave passes are again showing an open
eyewall on the west side. Intensity estimates range from 82 to 99
kt, so the initial wind speed will stay at 90 kt.

There are still hints of northerly shear in cirrus cloud motions
from the 1-min GOES-16 data, although the cyclone's cloud canopy
looks less distorted than yesterday.  This shear is forecast to
persist for the next day or two while the hurricane moves over
warm waters.  After that time, while the shear could decrease,
Hilary will be traversing marginally warm waters, with some increase
in drier, more stable air in the environment.  Most of the guidance
is in good agreement on little change in the short-term, with a
gradual decrease in wind speed through 3 days.  Beyond then, much
colder waters should cause a more rapid weakening, along with some
interaction with Irwin. The new NHC forecast is basically an update
of the previous one and lies close to IVCN, the variable intensity
model consensus. It should be noted that the ECMWF is on its own by
intensifying Hilary to a major hurricane in 2 to 3 days.

The initial motion is 280/11.  The track forecast is essentially
unchanged for the next 48 h, while Hilary is expected to be steered
by the mid-level subtropical ridge to the north.  After that time,
the ridge is forecast to become weaker to due to a mid- to
upper-level trough dropping over the Baja California peninsula.
Models are not in good agreement on how much the ridge weakens due
to this trough, leading to a wide disparity of solutions at long
range.  There has been little change in the guidance suite since 6z,
so the official forecast is close to the previous one.


FORECAST POSITIONS AND MAX WINDS

INIT  26/1500Z 16.4N 112.3W   90 KT 105 MPH
 12H  27/0000Z 16.7N 113.9W   90 KT 105 MPH
 24H  27/1200Z 17.1N 115.7W   90 KT 105 MPH
 36H  28/0000Z 17.5N 117.4W   85 KT 100 MPH
 48H  28/1200Z 18.1N 118.9W   80 KT  90 MPH
 72H  29/1200Z 19.7N 121.9W   75 KT  85 MPH
 96H  30/1200Z 21.4N 125.4W   55 KT  65 MPH
120H  31/1200Z 23.0N 129.0W   35 KT  40 MPH

$$
Forecaster Blake

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