Hurricane ISELLE

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HURRICANE ISELLE DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
200 PM PDT SAT AUG 02 2014

Despite continued north-northeasterly shear, Iselle has strengthened
to category 2 strength during the past few hours.  The deep
convection remains a little asymmetric, favoring the eastern
semicircle, but Dvorak estimates have still risen to T4.5/77 kt from
TAFB and T5.0/90 kt from SAB and the UW-CIMSS ADT.  These data,
combined with an earlier AMSU estimate of 78 kt, support raising the
initial intensity to 85 kt.

The vertical shear, such as it is, is still expected to diminish
during the next 12-24 hours.  At the same time, Iselle will be
moving over decreasing oceanic heat content values, and the stronger
winds will likely lead to increased upwelling of colder water.  The
official forecast allows for a little more intensification in the
short term, but after 24 hours the less favorable thermodynamic
environment should induce gradual weakening.  The updated NHC
intensity forecast is a little bit higher than the previous one only
during the first 3 days to account for the higher initial intensity.
Beyond day 3, the GFDL and HWRF keep Iselle near the threshold of
hurricane intensity while the statistical models show a more marked
decrease in winds. The NHC intensity forecast is very close to the
LGEM and FSU Superensemble on days 4 and 5.

Iselle's initial motion is 280/8 kt.  The hurricane is expected to
maintain a general westward motion but could slow down a bit in
48-72 hours when the ridge to the north of Iselle weakens.  By days
4 and 5, a mid-level high northeast of Hawaii is anticipated to
strengthen and slide eastward, which should impart a faster westward
motion at the end of the forecast period.  The track guidance is
tightly clustered during the first 72 hours, but most of the models,
particularly the ECMWF and GFDL, have shifted northward on this
cycle.  The updated NHC track forecast is also nudged northward on
days 4 and 5 and lies close to the FSU Superensemble.

FORECAST POSITIONS AND MAX WINDS

INIT  02/2100Z 15.1N 130.1W   85 KT 100 MPH
 12H  03/0600Z 15.4N 131.5W   90 KT 105 MPH
 24H  03/1800Z 15.7N 133.5W   90 KT 105 MPH
 36H  04/0600Z 15.9N 135.4W   85 KT 100 MPH
 48H  04/1800Z 16.0N 137.0W   80 KT  90 MPH
 72H  05/1800Z 16.0N 140.0W   75 KT  85 MPH
 96H  06/1800Z 16.5N 144.5W   60 KT  70 MPH
120H  07/1800Z 17.5N 150.5W   45 KT  50 MPH

$$
Forecaster Berg

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