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HURRICANE ISELLE DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
800 AM PDT SAT AUG 02 2014

Iselle has maintained an eye during the past several hours, but the
deepest convection has been unable to persist within the western
eyewall.  According to UW-CIMSS shear analyses, about 15 kt of
north-northeasterly shear is affecting the hurricane, and a recent
TRMM pass indicated that the mid-level center is displaced about
10-15 n mi south of the low-level center.  The maximum winds are
still estimated to be 70 kt based on Dvorak estimates of T4.5/77 kt
from SAB and T4.0/65 kt from TAFB.

Moderate vertical shear is expected to persist for another 12 hours
or so and then become negligible between 24-72 hours.  Even though
sea surface temperatures are expected to stay near or just above
26C through the next 5 days, oceanic heat content is forecast to
drop significantly in about 24-36 hours.  Therefore, mixing and
upwelling of colder water is likely to limit significant additional
strengthening.  The intensity models are in good agreement in
showing Iselle leveling off around 75 kt during the next couple of
days, and the official forecast maintains that scenario.  Cooler
ocean water and increased shear are expected to cause weakening
beyond day 3.

Iselle is located to the south of a mid-level ridge, which is
steering the hurricane westward with an initial motion of 280/9 kt.
A mid-level shortwave trough is still expected to develop to the
north of Iselle in about 48 hours, but its only real effect will be
to weaken the steering flow for a day or two.  After day 3,
mid-level ridging is forecast to restrengthen to the north and
northeast of Iselle, causing the cyclone to accelerate westward by
the end of the forecast period.  There continues to be some
latitudinal spread in the track guidance, especially on days 4 and
5.  The updated NHC track forecast is very near the previous
forecast and the model consensus TVCE for the sake of continuity.

FORECAST POSITIONS AND MAX WINDS

INIT  02/1500Z 15.0N 129.2W   70 KT  80 MPH
 12H  03/0000Z 15.2N 130.5W   75 KT  85 MPH
 24H  03/1200Z 15.6N 132.4W   75 KT  85 MPH
 36H  04/0000Z 15.9N 134.2W   75 KT  85 MPH
 48H  04/1200Z 16.0N 135.9W   75 KT  85 MPH
 72H  05/1200Z 16.0N 139.0W   70 KT  80 MPH
 96H  06/1200Z 16.0N 143.0W   60 KT  70 MPH
120H  07/1200Z 16.5N 148.5W   45 KT  50 MPH

$$
Forecaster Berg

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