684 
 WTPZ42 KNHC 242031
 TCDEP2
 
 TROPICAL STORM SANDRA DISCUSSION NUMBER   5
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP222015
 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.
 
 FORECAST POSITIONS AND MAX WINDS
 
 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