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Hurricane SEYMOUR Forecast Discussion

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WTPZ45 KNHC 241433

900 AM MDT MON OCT 24 2016

Seymour's cloud pattern continues to increase in organization.
The cyclone's small central dense overcast has become circular and
increasingly symmetric since the last advisory, with plenty of
cold-topped deep convection, particularly near the center.  Dvorak
satellite classifications were T3.5/55 kt and T4.0/65 kt at 1200
UTC, while UW-CIMSS ADT values were around T4.5.  Since that time,
the cloud pattern has continued to exhibit greater organization.
Thus, the initial intensity is raised to 65 kt, toward the higher
end of the subjective estimates.

For the next 36 hours or so, Seymour should be embedded in a nearly
ideal environment for intensification, characterized by low vertical
wind shear, warm waters, strong upper-level divergence and a
sufficiently moist atmosphere.  SHIPS model output continues to
indicate the likelihood of rapid intensification during the next
24 hours, and so does the official forecast.  Around 48 hours,
southwesterly shear associated with a vigorous trough northwest of
Seymour should begin to increase and induce weakening.  The shear
should become prohibitively high in 3 to 4 days and result in rapid
weakening, and then a decoupling of the cyclone toward the end of
the forecast period. Remnant low status is predicted in 5 days, but
it very likely could be sooner.  The NHC intensity forecast is
largely an update of the previous one and is slightly above the
multi-model consensus, close to the FSU Superensemble and the NOAA
corrected consensus model, HCCA.

The initial motion is 290/13.  Seymour is being steered west-
northwestward on the south side of deep-layer ridge near the
southern tip of the Baja California peninsula.  When the cyclone
reaches the western edge of this ridge in about 2 days, it should
encounter the flow associated with the deep-layer trough upstream
of Seymour.  This should result in a decrease in forward speed while
the cyclone's heading turns northwestward and then sharply
northward.  Once a completely shallow system, Seymour or its
remnants should turn north-northeast and lose its identity well west
of the Baja California peninsula.  The new track forecast has been
adjusted westward in response to a shift of the guidance in that
direction, but not as far left as the multi-model consensus.


INIT  24/1500Z 15.2N 109.8W   65 KT  75 MPH
 12H  25/0000Z 15.8N 111.9W   75 KT  85 MPH
 24H  25/1200Z 16.2N 114.5W   95 KT 110 MPH
 36H  26/0000Z 16.6N 116.9W  105 KT 120 MPH
 48H  26/1200Z 17.4N 119.0W   95 KT 110 MPH
 72H  27/1200Z 20.5N 121.8W   75 KT  85 MPH
 96H  28/1200Z 23.9N 121.5W   45 KT  50 MPH
120H  29/1200Z 26.2N 120.2W   25 KT  30 MPH...POST-TROP/REMNT LOW

Forecaster Kimberlain