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Tropical Storm Rosa Discussion Number  24
NWS National Hurricane Center Miami FL       EP202018
800 PM PDT Sun Sep 30 2018

All of Rosa's associated deep convection is located within the
northeastern quadrant of the circulation, moving out ahead of the
center due to 25-30 kt of southwesterly shear.  Subjective and
objective intensity estimates have decreased since the previous
advisory but encompass a wide range from about 45 kt to 65 kt. The
initial intensity is lowered to 55 kt, the average of these
estimates and similar to the latest UW-CIMSS SATCON estimate. Rosa's
center is now over sub-24C waters, heading for waters around 21C
along the Baja California coast, and the shear is forecast to
increase further in the coming days.  As a result, Rosa is expected
to weaken below tropical storm intensity between 24-36 hours, after
it has reached the Baja California coast.  All of the cyclone's deep
convection is likely to be sheared away soon thereafter, making Rosa
a remnant low between 36-48 hours, if not sooner.  The remnant low
should dissipate over Arizona by 48 hours.

Rosa continues to move north-northeastward, or 025/10 kt.  The flow
on the eastern side of a large mid-level trough located off the
U.S. West Coast should continue to steer Rosa north-northeastward,
with some acceleration beginning by Monday night.  Although there
are still some speed differences among the models, particularly
between the faster GFS and slower ECMWF, the guidance remains
tightly clustered overall, and the new NHC track forecast is very
close to the multi-model consensus aids.


Key Messages:

1. The main hazard expected from Rosa or its remnants is very heavy
rainfall in Baja California, northwestern Sonora, and the U.S.
Desert Southwest.  These rains are expected to produce
life-threatening flash flooding and debris flows in the deserts, and
landslides in mountainous terrain.  For more information about
potential rainfall in that area, please see products from the
Weather Prediction Center and your local NWS forecast office.

2. Tropical storm conditions are expected over portions of the
central and northern Baja California peninsula on Monday, possibly
spreading to the northern Gulf of California Monday night.
Interests in those locations should monitor the progress of Rosa.


FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 26.0N 117.6W   55 KT  65 MPH
 12H  01/1200Z 27.3N 116.8W   45 KT  50 MPH
 24H  02/0000Z 29.1N 115.6W   35 KT  40 MPH
 36H  02/1200Z 31.5N 114.1W   30 KT  35 MPH...NEAR THE SONORA COAST
 48H  03/0000Z 34.2N 112.4W   25 KT  30 MPH...POST-TROP/INLAND
 72H  04/0000Z...DISSIPATED

$$
Forecaster Berg

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