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 447 
 WTPZ42 KNHC 270845
 TCDEP2
 
 TROPICAL STORM MARTY DISCUSSION NUMBER   3
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172015
 400 AM CDT SUN SEP 27 2015
 
 ASCAT data from a few hours ago indicate that Marty's maximum winds
 have increased to 45 kt.  The center is embedded beneath a
 persistent burst of deep convection, and strong convective bands
 trail to the south and southwest of the central dense overcast.
 The structure suggests there could be a little bit of westerly
 shear, which UW-CIMSS and the SHIPS diagnostics are showing to be
 about 10-15 kt.
 
 Marty is over sea surface temperatures of at least 30 degrees
 Celsius, and the vertical shear is expected to be steady for the
 next 24 hours or so.  These conditions should allow the cyclone to
 continue strengthening, and in fact, rapid intensification is a
 possibility.  The SHIPS RI guidance is showing a 64 percent chance
 of a 25-kt increase in winds during the next 24 hours, and the
 SHIPS and LGEM models bring Marty at or just below hurricane
 intensity at that time.  The dynamical models are a little bit
 less aggressive with the future intensity, but given that Marty is
 already a little stronger from the get-go, the more aggressive
 statistical guidance seems to be the more likely scenario.
 Vertical shear is expected to increase by 36 hours, which is
 expected to lead to a quick weakening trend during the latter part
 of the forecast period.  The updated NHC intensity forecast is
 adjusted upward a bit through 48 hours to account for the higher
 initial intensity and the latest guidance, and is actually very
 similar to the Florida State Superensemble.
 
 Marty is located to the west of a mid-level ridge which extends
 across Central America, and to the south of a deep-layer trough
 located over Mexico and the southern United States.  This pattern
 is steering the cyclone northward, or 360/5 kt.  Marty should turn
 northeastward but slow down during the next 48 hours as the
 steering currents weaken.  After the vertical shear increases,
 possibly displacing the deep convection away from the center, the
 circulation is expected to stall and then turn westward between
 days 3 through 5, keeping the center just offshore of the coast of
 Mexico.  The GFS and the NAVGEM are the only models that bring
 Marty inland over Mexico, but these solutions do not appear likely
 at this time, especially since even the GFS ensemble mean stays
 offshore.  Despite these model differences, no significant changes
 were required to the NHC track forecast from the previous advisory.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  27/0900Z 14.3N 103.1W   45 KT  50 MPH
  12H  27/1800Z 15.0N 102.9W   55 KT  65 MPH
  24H  28/0600Z 15.6N 102.5W   65 KT  75 MPH
  36H  28/1800Z 16.0N 102.1W   65 KT  75 MPH
  48H  29/0600Z 16.2N 101.8W   60 KT  70 MPH
  72H  30/0600Z 16.5N 101.6W   40 KT  45 MPH
  96H  01/0600Z 17.0N 103.0W   30 KT  35 MPH
 120H  02/0600Z 16.5N 105.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
 $$
 Forecaster Berg
 
 
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