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Hurricane Hilary Discussion Number  22
NWS National Hurricane Center Miami FL       EP092017
300 PM MDT Wed Jul 26 2017

There haven't been many changes with Hilary during the past several
hours.  The hurricane continues to produce very deep convection,
although the cyclone remains a little lopsided on the right side.
Dvorak satellite estimates are a consensus T5.0 from TAFB & SAB, so
the winds will be kept at 90 kt.

Microwave data indicate that northerly shear is affecting Hilary,
with some displacement seen on the mid- and lower-level channels,
along with a weak northwest eyewall.  The shear is forecast to
linger for the next day or two while the hurricane moves over
warm waters.  Thereafter, while the shear should decrease,
Hilary will be moving across marginally warm waters, with an
increase in drier, more stable air in the environment expected.
Guidance remains in fairly good agreement on little change in
strength for the short-term, with a gradual decrease in wind speed
through day 3.  Notably, the ECMWF has backed off on its major
hurricane forecast for Irwin.  Beyond then, much cooler waters and a
dry stable air mass should cause a more rapid weakening, along with
some interaction with Irwin.  Little change was made to the previous
NHC forecast.

The initial motion is 280/11.  Hilary should move between west or
west-northwest during the next day or so while it is steered
by the mid-level subtropical ridge to the north.  After that time,
the ridge is forecast to become weaker due to a mid- to upper-level
trough dropping over the Baja California peninsula. Models are
having much difficulty on resolving these features, with
the ECMWF shifting over 400 n mi to the southwest on this run as
the cyclone gets hit by northerly flow west of the trough.  The GFS
continues on the northeast side of the guidance envelope as the
trough just weakens the ridge, allowing Hilary to move
northwestward. The official forecast is shifted somewhat westward
with the consensus but, since our best two models are on opposite
edges of the guidance envelope, this is a very low confidence
forecast.  This forecast has Hilary very close to Irwin at day 5.

FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 16.7N 113.2W   90 KT 105 MPH
 12H  27/0600Z 17.0N 114.7W   90 KT 105 MPH
 24H  27/1800Z 17.5N 116.5W   85 KT 100 MPH
 36H  28/0600Z 18.1N 118.1W   85 KT 100 MPH
 48H  28/1800Z 18.7N 119.7W   80 KT  90 MPH
 72H  29/1800Z 20.3N 123.3W   65 KT  75 MPH
 96H  30/1800Z 21.5N 126.5W   50 KT  60 MPH
120H  31/1800Z 23.0N 130.5W   35 KT  40 MPH

$$
Forecaster Blake

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