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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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