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HURRICANE HILDA DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP102015
200 PM PDT FRI AUG 07 2015

Hilda has undergone rapid intensification during the past several
hours, with a small eye forming in the middle of the central dense
overcast.  The initial intensity, however, is somewhat uncertain due
to a large spread in the satellite estimates.  Subjective Dvorak
estimates from TAFB and SAB are 55 kt and 65 kt, while the latest
AMSU estimates from CIMSS and CIRA are 75 kt and 60 kt.  In
addition, there is a CIMSS Satellite consensus estimate of about 60
kt.  Based on these data, the initial intensity is increased to 70
kt.  The shear observed this morning seems to have diminished, as
the outflow is increasing in the eastern semicircle.

The initial motion is slightly faster at 275/13.  For the next 48
hours or so, 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 generally
northwestward.  The track guidance again generally agrees on this
scenario, and while the GFDL and GFDN models remain right outliers
there is better overall agreement on how sharply Hilda will turn
than for the previous forecast.  The new forecast track is nudged a
little to the west of the previous track based mostly on the
current position and motion, and it lies near the consensus models
and the center of the guidance envelope.

It is unclear how long the current rapid intensification will last.
The Rapid Intensification Index of the SHIPS model shows about a
30 percent chance of a 25 kt increase in strength during the next
24 hours.  However, the cloud pattern of the hurricane still has a
ragged appearance, and due to the small size of the system any
unfavorable aspect of the environment could stop intensification.
The new forecast compromises between these extremes and calls for
continued strengthening at a slower rate through 36 hours.  After
48-72 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 remains in best overall
agreement with the intensity consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 12.7N 138.3W   70 KT  80 MPH
 12H  08/0600Z 13.0N 139.9W   75 KT  85 MPH
 24H  08/1800Z 13.7N 142.0W   80 KT  90 MPH
 36H  09/0600Z 14.4N 144.0W   85 KT 100 MPH
 48H  09/1800Z 15.2N 145.6W   85 KT 100 MPH
 72H  10/1800Z 17.0N 148.5W   75 KT  85 MPH
 96H  11/1800Z 19.0N 150.0W   60 KT  70 MPH
120H  12/1800Z 20.5N 151.5W   40 KT  45 MPH

$$
Forecaster Beven

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