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TROPICAL STORM SANDRA DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP222015
800 AM MST TUE NOV 24 2015

Sandra continues to gain organization, with the low-level center
embedded beneath a growing CDO feature, and an elongated convective
band wrapping around the northern semicircle.  In addition, a 0716
UTC GPM overpass indicated that the cyclone has tight inner-core low
cloud lines.  Subjective and objective satellite intensity estimates
range from T2.5/35 kt to T3.5/55 kt, and the maximum winds are
therefore raised to 45 kt.

The synoptic pattern consists of a mid-level ridge extending
westward from southern Mexico to 110W and a low-amplitude trough
north of 25N over the Pacific Ocean, with Sandra moving 280/11 kt
around the southwestern portion of the ridge.  The trough is
forecast to amplify and will cause Sandra to recurve around the
ridge during the next several days.  So far, the numerical models
have remained in excellent agreement for much of the forecast
period, with only minor speed differences between days 3 through 5
when Sandra gets picked up by the trough.  The NHC official track
was shifted only slightly westward beyond day 3 to fall closer to
the various model consensus aids, but otherwise no significant
changes to the previous forecast were required.

The environment appears well suited for Sandra to continue
strengthening during the next 48 hours.  Sea surface temperatures
along the forecast track will be between 29 and 30 degrees Celsius,
and the vertical shear is expected to be less than 10 kt for the
next two days.  Therefore, steady strengthening is shown through 48
hours, with Sandra potentially peaking as a category 2 hurricane
around that time.  This forecast is near the HWRF and Florida State
Superensemble, which are at the upper end of the guidance envelope.
Quicker strengthening than what is shown in the official forecast is
possible, with the Rapid Intensification Index showing about a 50
percent chance of a 30-kt increase in winds over the next 24 hours.
After 48 hours, southwesterly shear is expected to increase
substantially, which should cause Sandra to weaken quickly while it
approaches the coast of Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 11.2N 106.1W   45 KT  50 MPH
 12H  25/0000Z 11.8N 107.5W   55 KT  65 MPH
 24H  25/1200Z 12.6N 109.3W   65 KT  75 MPH
 36H  26/0000Z 13.6N 110.6W   75 KT  85 MPH
 48H  26/1200Z 15.1N 111.0W   85 KT 100 MPH
 72H  27/1200Z 19.1N 110.7W   70 KT  80 MPH
 96H  28/1200Z 23.0N 108.5W   45 KT  50 MPH
120H  29/1200Z 27.5N 105.0W   20 KT  25 MPH...POST-TROP/INLAND

$$
Forecaster Berg

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