649 
 WTPZ45 KNHC 260239
 TCDEP5
 
 Tropical Storm Rosa Discussion Number   4
 NWS National Hurricane Center Miami FL       EP202018
 900 PM MDT Tue Sep 25 2018
 
 Satellite imagery indicates that Rosa is still strengthening. The
 tropical storm has impressive banding features that wrap
 cyclonically from the northwest to northeast quadrant, though a dry
 slot has recently been observed infringing on the storm's developing
 inner-core. The most recent Dvorak intensity estimates from TAFB and
 SAB are 55 kt, so the initial intensity has been raised to that
 value.
 
 All of the intensity guidance suggests that rapid intensification
 (RI) is either already underway or imminent. SSMIS imagery from
 around 2300 UTC appeared to confirm the onset of RI with the
 development of a small low-level eye-like feature that has been
 associated with rapid intensification in past tropical cyclones.
 Although more recent imagery indicates this feature may have been
 disrupted by the aforementioned dry slot, the models suggest that
 this disruption may not last long. The NHC forecast therefore
 continues to show RI, and now calls for Rosa to become a major
 hurricane in about 36 h. Beyond that time, the hurricane is expected
 to remain in a fairly favorable environment through Friday, however,
 eyewall replacement cycles could limit the extent to which Rosa
 intensifies once it nears major hurricane strength. By the weekend,
 cooler SSTs and a drier surrounding environment should cause Rosa to
 begin weakening. The NHC intensity forecast is similar to the
 previous advisory, and is generally close to HCCA, especially beyond
 48 h.
 
 Rosa is moving steadily west-northwestward, or 285/8 kt.  A mid-
 level ridge to the north of Rosa should keep the cyclone on the
 same general heading for the next several days.  There is still some
 large discrepancies between the global models on the strength of the
 ridge for the next few days, resulting in differences in the forward
 speed of Rosa during that time. By the end of the week, a large
 mid-latitude trough is expected to create a weakness in the ridge,
 allowing Rosa to turn northwestward, and possibly northward. The NHC
 track forecast will continue to follow the TVCE and HCCA consensus
 aids for this advisory.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  26/0300Z 15.1N 109.7W   55 KT  65 MPH
  12H  26/1200Z 15.5N 110.9W   70 KT  80 MPH
  24H  27/0000Z 16.0N 112.5W   85 KT 100 MPH
  36H  27/1200Z 16.3N 114.1W  100 KT 115 MPH
  48H  28/0000Z 16.6N 115.8W  105 KT 120 MPH
  72H  29/0000Z 17.8N 119.0W  110 KT 125 MPH
  96H  30/0000Z 20.0N 120.4W   90 KT 105 MPH
 120H  01/0000Z 22.0N 121.0W   75 KT  85 MPH
 
 $$
 Forecaster Zelinsky
 
 

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