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Hurricane SEYMOUR Forecast Discussion

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WTPZ45 KNHC 262039

200 PM PDT WED OCT 26 2016

Seymour has begun to quickly weaken.  The hurricane's central dense
overcast has taken on a distorted appearance, and the deep
convection associated with the cyclone's circulation has become
noticeably asymmetric.  The eye has also become cloud-filled and
has cooled rather dramatically in the last few hours.  The recent
deterioration of the cloud pattern is associated with a considerable
increase of southwesterly shear over the cyclone.  Dvorak T-numbers
have decreased to T5.5/102 kt from both satellite agencies, and
these estimates averaged with Dvorak CI-numbers, are used to lower
the initial intensity to 110 kt.

The shear, currently analyzed in the 15 to 20 kt range, is forecast
to increase tremendously over Seymour during the next 24 to 36 hours
as a strong mid- to upper-level tropospheric trough approaches the
cyclone from the west. Since Seymour is a small tropical cyclone and
will be traversing cooler waters by that time, the weakening trend
should become increasingly more rapid. Global models show the vortex
decoupling as a result of the strong deep-layer shear in 30 to 36
hours, and the official forecast shows Seymour degenerating into a
remnant low by 48 hours.  The NHC track forecast represents an
update of the previous one and is near the various model consensus

Seymour continues to gain a greater northward component of motion,
and the initial motion estimate is 300/11.  The cyclone is forecast
to turn even more poleward and slow down during the next 24 to 36
hours as it rounds the western periphery of a mid-level high located
west of the Baja California peninsula.  While the vortex remains
intact, the strong south-southwesterly flow associated with the
upstream trough should cause Seymour to turn north-northeastward
before shearing off and eventually dissipating.  The NHC intensity
forecast is not much different than the previous one and near the
multi-model consensus.


INIT  26/2100Z 17.5N 121.2W  110 KT 125 MPH
 12H  27/0600Z 18.8N 122.2W   85 KT 100 MPH
 24H  27/1800Z 20.6N 123.0W   60 KT  70 MPH
 36H  28/0600Z 22.3N 122.6W   40 KT  45 MPH
 48H  28/1800Z 23.5N 121.7W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  29/1800Z...DISSIPATED

Forecaster Kimberlain