934 
 WTPZ45 KNHC 260845
 TCDEP5
 
 Tropical Storm Rosa Discussion Number   5
 NWS National Hurricane Center Miami FL       EP202018
 300 AM MDT Wed Sep 26 2018
 
 After steadily intensifying yesterday, Rosa's strengthening trend
 has temporarily paused.  The tropical storm has a well-defined
 curved band that wraps about three-quarters of the way around the
 center.  However, some dry air appears to be intruding into the core
 from the northeastern quadrant, which could be the reason why Rosa
 has stopped strengthening for now.  The Dvorak classifications from
 TAFB and SAB remain 3.5/55 kt, so the initial intensity is held at
 that value.  This wind speed is also close to the latest SATCON
 estimate from CIMSS at the University of Wisconsin.
 
 A strengthening trend is expected to resume soon, and it seems
 likely that Rosa will rapidly intensify during the next couple of
 days while it remains over warm SSTs and in an environment of low
 wind shear of 10 kt or less.  The NHC intensity forecast closely
 follows the HCCA model, and brings Rosa to hurricane strength later
 today and major hurricane strength on Thursday.  Beyond a few days,
 steady weakening is forecast due to cooler SSTs, dry and stable air,
 and an increase in southwesterly wind shear.
 
 The tropical storm is moving west-northwestward at 7 kt, steered by
 a mid-level ridge to its north.  A west to west-northwest motion at
 about the same forward speed is expected for the next couple of days
 as the pattern holds.  After that time, the ridge is expected to
 break down as a large, deep-layer low moves toward the U.S. west
 coast.  This change in the steering flow should cause Rosa to move
 northwestward late Friday and Saturday and then northward late in
 the weekend.  The models have come into a little better agreement
 this cycle, and a slight eastward shift has been made at 96- and
 120-hours based on this guidance.  This forecast lies fairly close
 to the various consensus aids.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  26/0900Z 15.5N 110.4W   55 KT  65 MPH
  12H  26/1800Z 15.9N 111.5W   70 KT  80 MPH
  24H  27/0600Z 16.2N 113.2W   85 KT 100 MPH
  36H  27/1800Z 16.5N 115.0W  100 KT 115 MPH
  48H  28/0600Z 16.8N 116.7W  105 KT 120 MPH
  72H  29/0600Z 18.3N 119.0W  105 KT 120 MPH
  96H  30/0600Z 20.7N 120.3W   85 KT 100 MPH
 120H  01/0600Z 23.0N 120.0W   65 KT  75 MPH
 
 $$
 Forecaster Cangialosi
 
 

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