Hurricane ISELLE

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HURRICANE ISELLE DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
800 PM PDT SAT AUG 02 2014

Iselle is still strengthening.  The central dense overcast has
become more symmetric since the last advisory, with cloud top
temperatures cooling slightly. The eye was also becoming better
defined but has recently become obscured by overshooting convective
tops.  Satellite intensity estimates from TAFB and SAB at 0000 UTC
were T5.0/90 kt and UW-CIMSS ADT values are at 5.4/99 kt.  These
data support increasing the initial intensity estimate to 95 kt.

The initial motion estimate is just north of due west or 275/09. A
subtropical ridge north of Iselle should allow the current motion to
persist in the short term.  However, a mid-latitude trough digging
roughly along 130W should temporarily weaken the ridge during the
next day or two, causing the forward speed of Iselle to nominally
decrease.  When the subtropical ridge rebuilds over the central
Pacific after day 3, Iselle should move on a westward and then
west-northwestward heading a faster forward speed.  The track
guidance is in relatively good agreement throughout the forecast
period, and the forecast track is adjusted only slightly to the
south in the direction of the multi-model consensus TVCE.

It is difficult to see Iselle strengthening much further.  Although
northeasterly shear over the cyclone is forecast to decrease during
the next couple of days, the thermodynamic contribution from the
environment should gradually become less favorable.  This would
suggest that some additional intensification is possible in the very
short term, followed by slow weakening after 24 hours.  The one
caveat would be that with little shear and marginally favorable
thermodynamic conditions Iselle could evolve into an annular
hurricane and maintain a somewhat higher intensity during the next
few days.  By days 4 and 5, even less favorable thermodynamic
factors and an uptick in south-southwesterly shear should result in
quicker weakening as Iselle approaches the Hawaiian Islands.  The
intensity forecast is somewhat higher than the previous one in the
short term and represents a blend of the multi-model consensus and
FSU Superensemble output.


FORECAST POSITIONS AND MAX WINDS

INIT  03/0300Z 15.2N 131.0W   95 KT 110 MPH
 12H  03/1200Z 15.4N 132.6W  100 KT 115 MPH
 24H  04/0000Z 15.6N 134.6W   95 KT 110 MPH
 36H  04/1200Z 15.7N 136.4W   90 KT 105 MPH
 48H  05/0000Z 15.8N 137.9W   85 KT 100 MPH
 72H  06/0000Z 15.9N 141.2W   75 KT  85 MPH
 96H  07/0000Z 16.6N 146.2W   60 KT  70 MPH
120H  08/0000Z 17.8N 152.4W   45 KT  50 MPH

$$
Forecaster Kimberlain

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