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Tropical Storm Hilary Discussion Number  27
NWS National Hurricane Center Miami FL       EP092017
800 PM PDT Thu Jul 27 2017

Deep convection associated with Hilary has been decreasing during
the last several hours, and the convective pattern is now limited to
a ragged central dense overcast.  This loss of convection appears to
be associated with dry air that has wrapped into the circulation, as
evident in microwave data.  An average of the latest Final T- and
CI-numbers from TAFB/SAB, along with ADT values from CIMSS at the
University of Wisconsin, support lowering the initial intensity to
60 kt, making Hilary a tropical storm.

Hilary still has another 18-24 hours over warm water, and the
regional hurricane models respond to this by showing Hilary
restrengthening during that time.  Given the observed weakening
trend over the past day or so and Hilary's current struggle with dry
air, the NHC intensity forecast lies at the low end of the guidance
during that time frame, and calls for the storm to remain steady in
intensity.  After 24 hours, Hilary is expected to cross the 26-deg C
isotherm and it will be moving over even cooler waters and into a
drier air mass during the next few days.  These unfavorable
conditions should cause weakening, and Hilary is forecast to become
a post-tropical cyclone in about 4 days.  The NHC intensity forecast
is similar to the previous one, and it lies fairly close to the
SHIPS and LGEM models.

The tropical storm is moving west-northwestward at 7 kt on the south
side of a mid-level ridge.  This motion with a slight increase in
forward speed is expected during the next couple of days as the
mid-level ridge strengthens.  When Irwin rotates around the eastern
and northern sides of Hilary in the 48- to 72-h time frame, Hilary
could turn briefly to the left before it absorbs Irwin.  Thereafter,
a slower motion to the west-northwest is predicted as the weakening
storm moves in the low- to mid-level flow.  The NHC track forecast
is adjusted a little to the north of the previous one, to come into
better agreement with the latest consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0300Z 18.3N 117.3W   60 KT  70 MPH
 12H  28/1200Z 18.8N 118.4W   60 KT  70 MPH
 24H  29/0000Z 19.6N 120.0W   60 KT  70 MPH
 36H  29/1200Z 20.5N 122.0W   55 KT  65 MPH
 48H  30/0000Z 21.2N 124.3W   55 KT  65 MPH
 72H  31/0000Z 22.1N 128.7W   45 KT  50 MPH
 96H  01/0000Z 23.2N 132.1W   35 KT  40 MPH...POST-TROPICAL
120H  02/0000Z 24.5N 134.8W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Cangialosi

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