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Hurricane ISELLE Forecast Discussion (Text)


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000
WTPZ44 KNHC 020238
TCDEP4

HURRICANE ISELLE DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
800 PM PDT FRI AUG 01 2014

Iselle's cloud pattern has increased in organization since the last
advisory, transitioning from a banding to an eye pattern. Cloud top
temperatures have also generally cooled in a small central dense
overcast that has recently formed. Though ragged and occasionally
obscured by high clouds, the 20 to 25 n mi diameter eye appeared
well defined in an earlier AMSR-2 microwave overpass.  Satellite
intensity estimates were 3.5 and 4.0 from TAFB and SAB at 0000 UTC,
respectively, with the latest ADT CI values at 4.0.  Based on these
data, the initial intensity is raised to 65 kt.

The initial motion estimate is 295/10.  Iselle should move steadily
west-northwestward on the south side of a subtropical ridge until a
mid- to upper-level trough digging along 130W in 2-3 days causes the
ridge to weaken.  Only a modest decrease in forward speed is
expected in at that time before the ridge re-strengthens over the
central Pacific by day 4, resulting in Iselle's moving faster
toward the west. The track guidance is tightly clustered through 2
days but diverges some after that time, with the guidance shifting
noticeably to the south at later times this cycle.  The official
track has been nudged a bit south in the short term and southward
even more by days 3-5, but is not as far south as the multi-model
consensus TVCE.

Iselle is likely to continue to intensify during the next day or
two.  The closed low-level ring of convection in microwave imagery
could portend a period of rapid intensification in the short term.
However, moderate north-northeasterly shear and marginal
thermodynamic parameters suggest this to be a lower probability
scenario.  After about 2 days, sea surface temperature drop below
26.5C and the environment is expected to gradually become even
drier and more stable later in the forecast period.  The shear
could also increase substantially by days 4-5 in association
with an upper-level trough, but this will depend on how far north
Iselle tracks.  The intensity forecast is higher than the previous
one through about 2 days but is unchanged at later times,
representing a blend of the multi-model consensus and the FSU
Superensemble output.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0300Z 14.7N 127.3W   65 KT  75 MPH
 12H  02/1200Z 15.1N 128.7W   70 KT  80 MPH
 24H  03/0000Z 15.5N 130.4W   75 KT  85 MPH
 36H  03/1200Z 15.8N 132.3W   75 KT  85 MPH
 48H  04/0000Z 16.2N 134.1W   75 KT  85 MPH
 72H  05/0000Z 16.4N 137.0W   65 KT  75 MPH
 96H  06/0000Z 16.5N 139.8W   60 KT  70 MPH
120H  07/0000Z 17.0N 144.5W   50 KT  60 MPH

$$
Forecaster Kimberlain



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Page last modified: Saturday, 02-Aug-2014 02:39:00 UTC