259 
 WTPZ45 KNHC 282055
 TCDEP5
 
 Hurricane Rosa Discussion Number  15
 NWS National Hurricane Center Miami FL       EP202018
 200 PM PDT Fri Sep 28 2018
 
 Rosa's appearance has rapidly deteriorated since this morning.
 There is still evidence of an ongoing eyewall replacement cycle,
 and an apparent moat region has occasionally been apparent in
 conventional satellite data during the past several hours.  The slow
 motion of the hurricane since last night could also be causing
 upwelling that would lead to further weakening.  Satellite
 intensity estimates from all agencies have dropped substantially
 accordingly, and the initial intensity has been lowered to 105 kt,
 based on a blend of Final-T and CI numbers from TAFB and SAB.
 
 Rosa is still moving northwestward, with an initial motion of
 325/5 kt. The model spread has increased a little, with the GFS and
 its associated regional models showing a slightly right (southeast)
 track, compared to earlier cycles, while the ECMWF has shifted an
 equal amount to the left (northwest). The consensus models have not
 changed much as a result of these offsetting model trends, so almost
 no change was made to the NHC track forecast. Rosa is still expected
 to turn northward, and then north-northeastward ahead of a mid- to
 upper-level trough approaching from the northwest.  The cyclone
 should then accelerate a little as it approaches the northern coast
 of the Baja California peninsula early next week.
 
 At this point, the structure of Rosa has degraded to the point that
 substantial restrengthening appears unlikely.  Since the hurricane
 still has about 24-36 hours before it reaches much cooler SSTs,
 only gradual weakening is forecast, though most of the intensity
 guidance shows more rapid weakening than currently indicated.
 After that time, a more rapid rate of weakening could occur due to
 cooler SSTs and an increase in wind shear associated with an
 upper-level trough approaching from the west.
 
 By early next week, Rosa is forecast to move inland over northern
 Baja California, and its surface circulation will likely dissipate
 shortly thereafter. However, moisture associated with Rosa is
 expected to spread northeastward through parts of the southwest
 United States.  For more information about potential rainfall in
 that area, please see products from the Weather Prediction Center
 and your local NWS forecast office.
 
 Key Messages:
 
 1. Rosa could bring tropical storm conditions to portions of the
 central and northern Baja California peninsula in a few days.
 Interests in those locations should monitor the progress of Rosa.
 
 2. Heavy rainfall associated with Rosa or its remnants is expected
 to affect parts of the southwest United States by early next week,
 which could cause flooding in this region.  For more information
 about potential rainfall and flooding, please see products from the
 Weather Prediction Center and your local NWS forecast office.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  28/2100Z 17.7N 117.8W  105 KT 120 MPH
  12H  29/0600Z 18.6N 118.3W   95 KT 110 MPH
  24H  29/1800Z 20.3N 118.8W   85 KT 100 MPH
  36H  30/0600Z 22.1N 118.9W   75 KT  85 MPH
  48H  30/1800Z 24.0N 118.4W   65 KT  75 MPH
  72H  01/1800Z 27.7N 116.8W   45 KT  50 MPH
  96H  02/1800Z 32.3N 114.5W   30 KT  35 MPH...INLAND
 120H  03/1800Z...DISSIPATED
 
 $$
 Forecaster Zelinsky
 
 

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