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Hurricane ISELLE


800 PM PDT MON AUG 04 2014

Iselle's cloud pattern has been in a remarkably steady state since
the last advisory.  The hurricane continues to maintain a classic
annular structure, with a large circular eye surrounded by a nearly
uniform ring of convection.  Satellite intensity estimates were
T6.0/115 kt at 0000 UTC from TAFB and SAB and UW-CIMSS ADT values
have also decreased to 6.0.  Based on these data and minor warming
of the cloud tops since that time, the initial intensity estimate is
lowered to 115 kt.

Iselle has jogged a little south of due west and slowed down during
the past six hours, and the initial motion estimate is 265/07. The
cyclone is forecast to continue on a slow westward course for the
next 12 hours or so in response to a mid-latitude trough briefly
weakening the subtropical ridge to the north of the cyclone.  After
that, Iselle should get caught under a building central Pacific
ridge with a slightly different orientation, which should result in
the cyclone's acceleration toward the west-northwest.  On the
forecast track, the center of Iselle should move near or over
portions of the Hawaiian Islands in 72-96 hours.  A slight
southward adjustment was made to the previous forecast track in the
direction of the multi-model consensus.

Iselle should retain its current annular characteristics during the
next 12 hour or so, and thus only slow weakening is likely.  After
that time, enough of an increase in southwesterly vertical shear and
the ingestion of drier and more stable air should disrupt the status
quo and result in steadier weakening.  Even further weakening should
occur by the time the center of Iselle approaches the Hawaiian
Islands in 48-72 hours, mostly as a result of a very dry air mass
in which the storm will be moving.  By 96-120 hours, the GFS/ECMWF
solutions show vertical shear increasing to nearly 30 kt which
results in a decoupling of the cyclone. The NHC intensity forecast
is lower than the previous one but above the multi-model consensus
through 48 hours and is a blend of the multi-model consensus and
LGEM output after that time.  Remannt low status is now indicated on
day 5.

Interests in the Hawaiian Islands should closely monitor the
progress of Iselle.  However, it is important not to focus too
closely on the exact track and intensity forecasts because the
average track error 72 hours out is about 100 miles, the average
intensity error is about 15 kt, and because the hazards of a
tropical cyclone can extend over a broad area often well away from
the center.

Iselle is expected to cross into the Central Pacific Hurricane
Center's area of responsiblity around 1800 UTC on Tuesday. Once
this occurs, the Central Pacific Hurricane Center in Honolulu,
Hawaii, will begin issuing advisories on Iselle.


INIT  05/0300Z 16.0N 138.0W  115 KT 135 MPH
 12H  05/1200Z 16.1N 139.2W  110 KT 125 MPH
 24H  06/0000Z 16.5N 141.4W   95 KT 110 MPH
 36H  06/1200Z 17.2N 144.3W   80 KT  90 MPH
 48H  07/0000Z 17.9N 147.7W   70 KT  80 MPH
 72H  08/0000Z 19.5N 154.3W   55 KT  65 MPH
 96H  09/0000Z 21.0N 160.2W   45 KT  50 MPH
120H  10/0000Z 22.0N 165.5W   30 KT  35 MPH...POST-TROP/REMNT LOW

Forecaster Kimberlain