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Hurricane Hilary Discussion Number  14
NWS National Hurricane Center Miami FL       EP092017
400 PM CDT Mon Jul 24 2017

Hilary continues to display a small central core with very deep
convective tops and lots of banding in the outer circulation.
Although an eye is not apparent in visible imagery, WindSAT
microwave data from earlier show that the hurricane has a distinct
eye underneath the cloud canopy.  Satellite estimates continue to
increase, so the initial wind speed is set to 75 kt, close to the
latest SAB fix.

The hurricane has been strengthening quickly during the past 24 h,
near the threshold of rapid intensification.  With no significant
changes to the favorable oceanic and atmospheric environments
forecast, there is good reason to show a similar rate of
strengthening for the first 24 hours of the forecast.  After that
time, models are indicating an increase in northerly wind shear,
partially associated with an enhanced anticyclonic outflow from TS
Irwin. This might limit the peak intensity, so the wind speed
forecast has been leveled off on day 2.  The latest model guidance
has come in closer to the previous official forecast, so little
change has been made in the new NHC intensity prediction.  Some
weakening is likely at longer range due to cooler SSTS, entrainment
of drier air, and binary interaction with Irwin.

The initial motion estimate is 300/7 kt.  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 little to the left and a bit faster during that time.
The long-range forecast is quite challenging with the threat of
binary interaction with Irwin, leading to widely divergent solutions
by days 4-5.  While the GFS keeps Hilary far separated from Irwin on
the northeastern side of the guidance envelope, its ensemble mean is
much more in the pack of the guidance, suggesting the latest GFS
solution is not very likely.  The UKMET and ECMWF continue to show
rare TC binary interaction and merger scenarios which, although
scientifically pleasing to see, lead to large errors potentially.
Overall, the model trend toward more interaction with Irwin
continues, which led to a westward shift of the latest NHC
prediction at days 3-5.

FORECAST POSITIONS AND MAX WINDS

INIT  24/2100Z 14.5N 104.9W   75 KT  85 MPH
 12H  25/0600Z 14.9N 106.0W   85 KT 100 MPH
 24H  25/1800Z 15.5N 107.8W  100 KT 115 MPH
 36H  26/0600Z 16.1N 110.0W  105 KT 120 MPH
 48H  26/1800Z 16.6N 112.0W  105 KT 120 MPH
 72H  27/1800Z 17.7N 115.8W   95 KT 110 MPH
 96H  28/1800Z 18.7N 119.3W   80 KT  90 MPH
120H  29/1800Z 19.5N 122.5W   70 KT  80 MPH

$$
Forecaster Blake

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