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TROPICAL STORM HILDA DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102015
800 AM PDT FRI AUG 07 2015

Infrared satellite data, along with VIIRS moonlight visible imagery
and a just received AMSR-2 overpass, show that Hilda is maintaining
strong convection near the center.  However, the system continues to
have a sheared appearence, which is somewhat surprising since the
available data show less than 10 kt of shear.  The various satellite
intensity estimates range between 45-55 kt, so the initial intensity
remains 50 kt.  The cirrus outflow is good to the west and poor to
the east.

The initial motion is 275/11.  For the next 48-72 hours, Hilda
should be steered westward to west-northwestward by the deep-layer
subtropical ridge to its north.  After that time, a mid- to
upper-level low is expected to develop north of the Hawaiian
Islands, which should cause Hilda to turn northwestward and
north-northwestward.  The track guidance again generally agrees
on this scenario, but there remains a significant spread in how
sharply Hilda will turn based on the strength of the cyclone after
72 hours.  The GFS, GFDL, and GFDN, which depict a stronger cyclone,
have sharper turns and end up on the east side of the guidance
envelope.  The ECMWF, HWRF, and GFS ensemble mean forecast a weaker
Hilda, and they show a more westward motion.  The UKMET and the
various consensus models are between these extremes.  The new
forecast track, which is little changed from the previous track,
follows this part of the guidance.

The dynamical models are in good agreement that whatever shear is
occurring should diminish in 24 hours or less.  This should allow a
faster rate of development, with Hilda forecast to become a
hurricane in 24-36 hours and reach its peak intensity in 48-72
hours.  After 72 hours, the cyclone is expected to encounter strong
southwesterly vertical shear and decreasing sea surface
temperatures, and this combination should cause significant
weakening.  The new intensity forecast has minor adjustments from
the previous forecast and is in best overall agreement with the
intensity consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 12.8N 136.7W   50 KT  60 MPH
 12H  08/0000Z 13.0N 138.3W   55 KT  65 MPH
 24H  08/1200Z 13.6N 140.5W   60 KT  70 MPH
 36H  09/0000Z 14.3N 142.5W   70 KT  80 MPH
 48H  09/1200Z 15.1N 144.5W   75 KT  85 MPH
 72H  10/1200Z 16.5N 147.5W   75 KT  85 MPH
 96H  11/1200Z 18.5N 149.5W   55 KT  65 MPH
120H  12/1200Z 20.5N 150.5W   40 KT  45 MPH

$$
Forecaster Beven

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