Tropical Storm SANDRA Forecast Discussion (Text)

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WTPZ42 KNHC 242031

200 PM MST TUE NOV 24 2015

Visible satellite imagery suggests that Sandra is strengthening
quickly.  Deep convection has recently blossomed in a ring around a
relatively clear region near the center, with a warm spot also
noted in infrared imagery.  Dvorak intensity estimates have risen to
T3.0/45 kt from SAB, T3.5/55 kt from TAFB, and T4.0/65 kt
from the UW-CIMSS ADT.  Therefore, the initial intensity is raised
to 55 kt.

Sandra has turned west-northwestward with an initial motion of
290/12 kt.  A mid-level ridge currently extends from southern Mexico
westward over the Pacific Ocean but an amplifying mid- to upper-
level trough near the U.S. west coast should erode the western
portion of the ridge during the next 24-48 hours.  This should cause
Sandra to recurve to the north and northeast during the forecast
period.  For the most part, the track guidance has been consistent
and has not shifted much to the right or left from cycle to cycle.
However, the latest guidance has trended a little faster than in
previous runs.  The updated NHC track forecast is pushed a little
faster close to the model consensus aids, and also a little bit
westward after 48 hours in deference to the ECMWF model, which is on
the western edge of the guidance envelope.

Based on the recent evolution of Sandra's cloud pattern, it appears
the storm could be going through a period of rapid intensification.
Sandra is over sea surface temperatures around 30 degrees Celsius
and in an environment of low shear, and the SHIPS RI index is around
50 percent for a 30-kt increase in winds during the next 24 hours.
Therefore, the NHC official forecast now shows the cyclone reaching
hurricane intensity tonight and peaking as a category 2 hurricane
in 36-48 hours.  Thereafter, vertical shear is expected to increase
from around 10 kt at 48 hours to 50-60 kt at 96 hours, which should
cause Sandra to weaken quickly as it approaches the coast of
Mexico.  The NHC intensity forecast is a little higher than the
previous forecast and is close to the HWRF model, which shows the
highest peak intensity among the guidance suite.

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.  However, a watch may be required on Wednesday,
and interests in those areas should monitor the progress of Sandra.


INIT  24/2100Z 11.9N 107.2W   55 KT  65 MPH
 12H  25/0600Z 12.5N 108.6W   65 KT  75 MPH
 24H  25/1800Z 13.5N 110.1W   80 KT  90 MPH
 36H  26/0600Z 15.1N 110.9W   90 KT 105 MPH
 48H  26/1800Z 16.9N 111.3W   90 KT 105 MPH
 72H  27/1800Z 21.1N 110.3W   65 KT  75 MPH
 96H  28/1800Z 25.5N 106.5W   30 KT  35 MPH...INLAND
120H  29/1800Z...DISSIPATED

Forecaster Berg

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Page last modified: Tuesday, 24-Nov-2015 20:31:59 UTC