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Hurricane SANDRA Forecast Discussion

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WTPZ42 KNHC 251435

800 AM MST WED NOV 25 2015

Sandra's convective pattern continues to become better organized,
and a pinhole eye was observed in a 1201 UTC SSMIS microwave pass.
An eye has also been apparent in the latest infrared satellite
images.  The intensity is increased to 85 kt based on Dvorak
estimates of T5.0/90 kt from TAFB and T4.8/85 kt from the UW-CIMSS
ADT.  This intensity makes Sandra the strongest hurricane in the
eastern North Pacific Ocean for this late in the year (the previous
record was Hurricane Winnie of 1983, which reached an intensity of
80 kt on December 6).

Low shear and warm sea surface temperatures should allow additional
strengthening, and the SHIPS Rapid Intensification Index is still
showing a 3 in 4 chance of a 30-kt increase during the next 24
hours.  Therefore, the NHC official forecast continues to show
Sandra reaching major hurricane strength during the next 12-24
hours, in best agreement with the SHIPS and LGEM models.
Southwesterly shear is expected to increase to about 30 kt by 48
hours, and even higher thereafter, which should induce a fast
weakening trend as Sandra approaches the Baja California peninsula
and west coast of Mexico.  The official intensity forecast after 24
hours is generally an update of the previous forecast and very close
to the IVCN intensity consensus.

The hurricane appeared to take a short-term jog to the west during
the past 6-12 hours, but the longer-term average motion is still
295/9 kt.  A subtropical ridge continues to extend from southern
Mexico westward to near 20N110W, but the ridge is expected to be
shunted eastward during the next 24 hours by an amplifying mid- to
upper-level trough near the west coast of North America.  This
should cause Sandra to turn northwestward and northward during the
next 36 hours and then northeastward by 96 hours.  The track
guidance is tightly clustered for the first 36 hours, but the
spread increases after that time.  The models which maintain a
deeper circulation (i.e., the GFS and HWRF) show a sharper and
faster recurvature, while the models which depict a weakening,
shallower system (i.e., the ECMWF and UKMET) show a slower and more
gradual recurvature.  Since fast weakening is expected after 48
hours, the updated NHC track forecast is slowed down and shifted a
bit westward during that period to be closer to the models that show
a faster weakening trend.

Although Sandra is forecast to weaken, it is too soon to know
exactly how Sandra will affect portions of the southern Baja
California peninsula or the west coast of mainland Mexico.  A watch
may be required later today or tonight for portions of Mexico, and
interests in those areas should monitor the progress of Sandra.


INIT  25/1500Z 12.6N 109.5W   85 KT 100 MPH
 12H  26/0000Z 13.5N 110.3W   95 KT 110 MPH
 24H  26/1200Z 15.1N 110.9W  105 KT 120 MPH
 36H  27/0000Z 16.9N 111.1W   95 KT 110 MPH
 48H  27/1200Z 18.7N 110.9W   80 KT  90 MPH
 72H  28/1200Z 22.5N 109.7W   40 KT  45 MPH
 96H  29/1200Z 26.0N 106.5W   20 KT  25 MPH...POST-TROP/INLAND
120H  30/1200Z...DISSIPATED

Forecaster Berg