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Hurricane Hilary Discussion Number  13
NWS National Hurricane Center Miami FL       EP092017
1000 AM CDT Mon Jul 24 2017

Satellite images indicate that Hilary has a small central core of
convection, with both the visible and infrared channels suggesting
that an eye is trying to form.  Microwave data also show an
incomplete eyewall, though the system is so small that most
sensors don't have the necessary resolution to really see the
center.  The initial wind speed is set to 70 kt, a bit above the
satellite fixes given the recent upward organization trend.
Interestingly, despite the hurricane having intensified about 30 kt
in the past 24 hours, model guidance this morning really backed off
on the future strengthening of Hilary, with most guidance no
longer showing it becoming a major hurricane.  It is difficult to
believe the new model runs because the environment seems similarly
favorable for at least the next day or so, with perhaps some
increase in northerly shear in about 48 hours. For now, the latest
NHC forecast is reduced just a little bit beyond 24 hours, owing to
the possible increase in shear, but still lies at or above all of
the guidance.

The initial motion estimate is 295/7.  A ridge that extends into the
eastern Pacific from the southwestern United States is forecast to
strengthen slightly over the next couple of days, which should
steer Hilary a bit faster to the west-northwest during that time.
The long-range forecast is a mess with the likelihood of some binary
interaction with TS Irwin, leading to a large model spread by day 5.
Dynamical guidance has been trending toward more interaction,
although the GFS/HMON models are well off to the northeast of the
rest of the guidance. The NHC prediction is close to the previous
one, putting a little more weight on the binary interaction
solutions, which results in a small westward shift of the forecast
at long range.  Obviously this type of forecast has large
uncertainty.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 14.1N 104.2W   70 KT  80 MPH
 12H  25/0000Z 14.6N 105.4W   80 KT  90 MPH
 24H  25/1200Z 15.2N 107.0W   95 KT 110 MPH
 36H  26/0000Z 15.9N 108.9W  105 KT 120 MPH
 48H  26/1200Z 16.5N 110.9W  110 KT 125 MPH
 72H  27/1200Z 17.7N 114.9W  100 KT 115 MPH
 96H  28/1200Z 18.7N 118.5W   85 KT 100 MPH
120H  29/1200Z 19.5N 121.5W   70 KT  80 MPH

$$
Forecaster Blake

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