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Hurricane Hilary Discussion Number  15
NWS National Hurricane Center Miami FL       EP092017
1000 PM CDT Mon Jul 24 2017

Recent microwave satellite images indicate that Hilary has developed
a tight banding eye feature with a diameter of less than 10 nmi.
Deep convection with cloud tops to -85C within an elongated CDO has
continued to pulse since the previous advisory, likely due to some
modest high-level shear induced by a large convective complex
located a couple hundred nmi southeast of Hilary's center. However,
that convective cloud mass has recently been showing signs of
waning, so that negative influence will likely begin to abate fairly
soon. Dvorak satellite intensity estimates were a consensus T4.5/77
kt from TAFB and SAB at 0000Z. Since that time, the CDO has become
more distinct and NHC objective intensity estimates have been
ranging between 82-88 kt during the past 2 hours. As a result, the
advisory intensity has been increased to 85 kt.

The initial motion estimate is 300/08 kt. Hilary is forecast to
move generally west-northwestward along the southern periphery of a
deep-layer subtropical ridge for the next 5 days. With the exception
of the more northerly GFS model -- which had a similar poleward bias
with Fernanda -- the rest of the NHC model guidance is tightly
clustered around the previous forecast track. As a result, only
minor speed adjustments were made to the previous forecast track.
Although some binary interaction with TS Irwin is still possible,
Hilary is expected to be the larger and more dominant circulation,
resulting in Irwin being pulled poleward within Hilary's wake on
days 3-5.

The small eye and tight inner-core banding features noted in recent
microwave imagery, along with large-scale low vertical wind shear
conditions and favorable thermodynamics, argues for some rapid
intensification to occur during the next 12-24 hours. Thereafter,
some adjustment of the eye and inner-core wind field is possible,
which has resulted in a leveling off of Hilary's intensity forecast
in the 24-to 48-h period. By 72 hours and beyond, the combination
of decreasing SSTs to less than 26C along with some modest westerly
wind shear should produce steady weakening. The official intensity
forecast is similar to the previous advisory, and follows a blend of
the HCCA and ECMWF intensity predictions.

FORECAST POSITIONS AND MAX WINDS

INIT  25/0300Z 15.0N 105.7W   85 KT 100 MPH
 12H  25/1200Z 15.5N 107.0W   95 KT 110 MPH
 24H  26/0000Z 16.1N 109.0W  105 KT 120 MPH
 36H  26/1200Z 16.5N 111.1W  105 KT 120 MPH
 48H  27/0000Z 17.1N 113.0W  100 KT 115 MPH
 72H  28/0000Z 18.1N 116.7W   90 KT 105 MPH
 96H  29/0000Z 19.1N 120.2W   80 KT  90 MPH
120H  30/0000Z 19.9N 123.4W   65 KT  75 MPH

$$
Forecaster Stewart

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