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Hurricane Rosa Discussion Number  10
NWS National Hurricane Center Miami FL       EP202018
800 AM PDT Thu Sep 27 2018

Rosa is becoming better organized.  Conventional satellite imagery
show a large area of cold cloud tops near the center, and there is
a hint of an eye in the first-light visible images.  Microwave
imagery indicates that the eye structure underneath the overcast
has become better defined, with less evidence of dry air entrainment
than seen yesterday.  The initial intensity has been increased to
90 kt in best agreement with the subjective Dvorak estimate from
TAFB and the CIMSS ADT technique.  The hurricane currently has good
outflow in all directions.

Conditions appear generally favorable for continued strengthening
for the next 24-36 hr, and the new intensity forecast now makes Rosa
a major hurricane in 12 h.  It should be noted that if the current
strengthening is the start of the previously anticipated rapid
intensification Rosa could get stronger than the current forecast,
which shows a peak intensity of 105 kt near the upper edge of the
intensity guidance.  After 36 h, the forecast track takes the
cyclone over decreasing sea surface temperatures, and by the end of
the forecast period it is expected to encounter strong southwesterly
vertical shear.  This combination should cause significant
weakening, and Rosa is expected to be a tropical storm as it
approaches the Baja California peninsula near the end of the
forecast period.

The initial motion is a somewhat uncertain 270/10.  For the next
12-24 h, the hurricane should move generally westward on the south
side of the subtropical ridge over the Pacific west of northern
Mexico and a mid-latitude ridge over California.  Subsequently, Rosa
should turn northwestward and northward through a break in the ridge
caused by a large mid-latitude trough moving eastward through the
northeastern Pacific.  By 96-120 h, Rosa should recurve
northeastward into the westerlies on the eastern side of the trough
and move in the general direction of northwestern Mexico and the
northern Baja California peninsula.  There remains some spread in
the guidance forward speed after recurvature, with the GFS being
faster than the ECMWF.  The new intensity forecast is a blend of
these extremes in forward speed at the 96 and 120 h points.
Overall, the guidance envelope has shifted a little west since the
previous advisory, and the new track is also shifted a little
westward.

FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 17.2N 115.4W   90 KT 105 MPH
 12H  28/0000Z 17.3N 116.9W  100 KT 115 MPH
 24H  28/1200Z 17.5N 118.1W  105 KT 120 MPH
 36H  29/0000Z 18.3N 119.0W  105 KT 120 MPH
 48H  29/1200Z 19.5N 119.4W  100 KT 115 MPH
 72H  30/1200Z 22.5N 119.5W   80 KT  90 MPH
 96H  01/1200Z 26.0N 118.0W   60 KT  70 MPH
120H  02/1200Z 29.5N 115.5W   40 KT  45 MPH

$$
Forecaster Beven

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