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Hurricane ROSA


Hurricane Rosa Discussion Number  11
NWS National Hurricane Center Miami FL       EP202018
200 PM PDT Thu Sep 27 2018

Rosa is undergoing rapid intensification, accompanied by the
formation of a well-defined 15 n mi wide eye inside the central
dense overcast.  Recent subjective and objective satellite intensity
estimates are generally in the 100-115 kt range, and the initial
intensity is increased to 110 kt in best agreement with the CIMSS
ADT and the subjective Dvorak estimate from TAFB.  Rosa continues to
have good cirrus outflow in all directions.

The intensity forecast has some complexities.  The first is how much
more Rosa will strengthen before the rapid intensification stops.
The new intensity forecast follows the upper edge of the guidance in
showing about 12 h more strengthening with a peak intensity of
120 kt.  That being said, it would not be surprising if Rosa got
stronger than that.  The simplest part of the forecast is from 24-72
h, when the sea surface temperatures cool along the forecast track
with Rosa gradually weakening as a result.  After 72 h, the cyclone
should move across the quite cold waters of the northeastern
Pacific, and then move across Baja California over the warm water of
the Gulf of California.  While that is happening, a mid-latitude
trough to the northwest is expected to cause both strong shear and
strong upper-level divergence over Rosa.  The intensity guidance
responds to this combination of ingredients with intensity forecasts
of anywhere between 30-65 kt as Rosa makes landfall on the Baja
California peninsula.  The new intensity forecast continues to call
for Rosa to weaken to a tropical storm before reaching Baja
California.  However, this should be considered to be a low
confidence forecast at this time.

Rosa is farther south than estimated in the previous advisory, and
the new initial motion is now 265/9.  Other than that, there is no
change in the forecast philosophy from the previous forecast.  For
the next 12 h or so, 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 the aforementioned 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 the
northern Baja California peninsula and northwestern Mexico.  The
dynamical models show spread in both direction and speed as Rosa
approaches Baja.  The ECMWF and the Canadian models are on the left
side of the envelope in forecasting landfall on the northern part of
the peninsula, while the GFS and the HWRF are on the right side with
a landfall closer to the central part of the peninsula. The new
forecast track lies between those extremes near the center of the
guidance envelope and the consensus models.


INIT  27/2100Z 16.9N 115.9W  110 KT 125 MPH
 12H  28/0600Z 17.0N 117.0W  120 KT 140 MPH
 24H  28/1800Z 17.5N 118.1W  120 KT 140 MPH
 36H  29/0600Z 18.4N 118.7W  115 KT 130 MPH
 48H  29/1800Z 19.8N 119.0W  105 KT 120 MPH
 72H  30/1800Z 23.5N 119.0W   85 KT 100 MPH
 96H  01/1800Z 26.5N 117.0W   60 KT  70 MPH
120H  02/1800Z 31.0N 114.0W   40 KT  45 MPH

Forecaster Beven