Tropical Storm ISELLE

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TROPICAL STORM ISELLE DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
200 PM PDT FRI AUG 01 2014

Iselle has a well-defined structure in visible imagery and at times
seems to have been trying to form an eye.  However, the convective
pattern as observed in infrared satellite imagery has been a little
ragged and not as well structured.  Dvorak estimates from TAFB and
SAB are now unanimously T3.5/55 kt, but final-T estimates from the
UW-CIMSS ADT have actually dropped to T3.1/47 kt since this
morning.  Based on these numbers, as well as a 50-kt estimate from
a recent ASCAT-B pass, the initial intensity is held at 55 kt.

The strengthening trend may be taking a temporary respite, but
environmental conditions should support further intensification
during the next 2-3 days.  Modest northerly shear appears to be
impinging on the storm, but that shear is expected to diminish in a
day or two.  By that time, thermodynamic conditions will become a
little more marginal as Iselle approaches the 26C sea surface
temperature isotherm.  The intensity models are in fairly good
agreement in showing modest strengthening, although the peak
intensities have decreased a bit.  Based on the latest guidance,
the updated NHC intensity forecast shows Iselle reaching a maximum
intensity of 70 kt in 36-48 hours.

The track models are also in good agreement, showing very little
spread during the first 3 days.  The subtropical ridge to the north
of Iselle should keep the cyclone on a west-northwestward track
during that time.  Iselle's forward speed is then expected to slow
down on days 3 and 4 as it gets impeded by a mid-level ridge near
Hawaii, and then speed up again on day 5 when the ridge slides
eastward.  No significant changes were required to the official
track forecast, and the NHC points continue to lie very close the
model consensus TVCE.

FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 14.5N 126.4W   55 KT  65 MPH
 12H  02/0600Z 14.9N 127.7W   60 KT  70 MPH
 24H  02/1800Z 15.4N 129.5W   65 KT  75 MPH
 36H  03/0600Z 15.9N 131.3W   70 KT  80 MPH
 48H  03/1800Z 16.3N 133.2W   70 KT  80 MPH
 72H  04/1800Z 16.6N 136.3W   65 KT  75 MPH
 96H  05/1800Z 16.9N 138.7W   60 KT  70 MPH
120H  06/1800Z 17.5N 143.0W   50 KT  60 MPH

$$
Forecaster Berg

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