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Hurricane SEYMOUR Forecast Discussion

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WTPZ45 KNHC 242104 CCA

300 PM MDT MON OCT 24 2016


Seymour is rapidly intensifying.  A pinhole eye has formed within a
small, nearly symmetric, central dense overcast (CDO) during the
last several hours.  In addition, a long curved band coils inward
toward the center with a dry slot between it and the CDO.  Dvorak
classifications are T4.5/77 kt from TAFB and SAB, and the latest
UW-CIMSS ADT value is T4.7/82 kt.  A blend of these is used to raise
the initial intensity estimate to 80 kt.

Seymour has another 24 hours to strengthen under nearly ideal
environmental conditions, consisting of low vertical wind shear,
warm waters, strong upper-level divergence, and a sufficiently moist
atmosphere.  By 36 to 48 hours,  an uptick in the southwesterly
vertical shear associated with a mid- to upper-tropospheric trough
approaching Seymour from the northwest should induce a weakening
trend.  With the waters cooling substantially and the shear becoming
prohibitively high after that time, rapid weakening is likely.
Seymour is now forecast to become a post-tropical remnant low by 96
hours, if not perhaps sooner, as depicted in global model guidance.
The new intensity forecast is generally above the the guidance
through 48 hours, closest to the FSU Superensemble and NOAA
Corrected Consensus HCCA model output, and just above the multi-
model consensus after that time.

The initial motion estimate is 285/14 kt. Seymour should maintain a
west-northwestward motion with some decrease in forward speed for
the next 36 to 48 hours as it nears the western periphery of a
mid-level ridge located to the south of Baja California.  The trough
upstream of Seymour should erode the ridge further in about 48 hours
and cause the cyclone to turn northwestward and northward while it
decelerates. The guidance has again shifted toward the left during
the next few days, and the official forecast is adjusted in that
direction but lies on the eastern side of the guidance envelope. The
model guidance is now much slower after that time, around the time
Seymour decouples and becomes a remnant low.


INIT  24/2100Z 15.3N 111.3W   85 KT 100 MPH
 12H  25/0600Z 15.6N 113.3W  100 KT 115 MPH
 24H  25/1800Z 16.0N 115.9W  110 KT 125 MPH
 36H  26/0600Z 16.7N 118.3W  110 KT 125 MPH
 48H  26/1800Z 17.6N 120.4W  100 KT 115 MPH
 72H  27/1800Z 20.7N 122.4W   70 KT  80 MPH
 96H  28/1800Z 22.3N 122.4W   35 KT  40 MPH...POST-TROP/REMNT LOW
120H  29/1800Z...DISSIPATED

Forecaster Kimberlain