Hurricane ISELLE

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HURRICANE ISELLE DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
800 PM PDT SUN AUG 03 2014

Iselle's satellite appearance has essentially been steady state
since the last advisory.  The cyclone continues to exhibit many of
the characteristics of an annular hurricane, with a nearly
axisymmetric convective structure and a curious lack of convective
features outside the well-defined cental dense overcast. A circular
but cloud-filled 20-25 n mi wide eye is also evident in last-light
visible imagery.  The initial intensity is reduced only slightly to
95 kt in accordance with the latest CI numbers from TAFB and SAB.

The initial motion estimate is a steady 280/10, with perhaps more of
a due-west wobble during the last couple of hours.  A mid-latitude
trough extending southwestward along 130w is forecast to weaken the
subtropical ridge north of Iselle during the next 24 hours.  The
effect of the weakened ridge should be a decrease in the cyclone's
forward motion for a brief period during the next day or two as it
approaches 140w.  By day 3, the cyclone should find itself south of
a newly established central Pacific ridge, which should steer Iselle
west-northwestward at a considerably faster forward speed by days
4-5.  The track forecast is little changed from the previous one
and is in the middle of the guidance envelope, very close to the
multi-model consensus TVCE.

Even though Iselle is moving over marginally warm sea surface
temperatures, its current annular structure in a very light-shear
environment suggests that the cyclone might retain a higher
intensity than the guidance might suggest if the large-scale
environmental conditions do not vary much at least during the next
day or possibly two. After that, significantly less favorable
thermodynamic factors, such as increasingly drier and more stable
air and water temperatures just below 26C, should result in
weakening while Iselle nears the Hawaiian Islands.  An accelerated
weakening may take place as Iselle makes its closest approach to the
Hawaiian chain when environmental conditions become even more
hostile.  The intensity forecast is about the same as the previous
one and is near the multi-model consensus IVCN and the SHIPS/LGEM
output.


FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 15.9N 134.8W   95 KT 110 MPH
 12H  04/1200Z 16.0N 136.2W   90 KT 105 MPH
 24H  05/0000Z 16.0N 137.8W   85 KT 100 MPH
 36H  05/1200Z 16.0N 139.3W   80 KT  90 MPH
 48H  06/0000Z 16.5N 141.3W   75 KT  85 MPH
 72H  07/0000Z 18.1N 146.8W   60 KT  70 MPH
 96H  08/0000Z 20.1N 153.1W   45 KT  50 MPH
120H  09/0000Z 22.3N 159.2W   40 KT  45 MPH

$$
Forecaster Kimberlain

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