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Hurricane Rosa Discussion Number  16
NWS National Hurricane Center Miami FL       EP202018
800 PM PDT Fri Sep 28 2018

The satellite appearance of Rosa continues to degrade due to an
ongoing eyewall cycle with weaker convection noted near the
eyewall and an apparent moat region.  Dvorak estimates continue to
fall, and a blend from all agencies gives 95 kt as an initial wind
speed.  Continued weakening is in the forecast while Rosa moves
across progressively cooler SSTs into a higher shear and drier
environment.  There is some chance that the weakening could pause if
the eyewall cycle finishes, but that's less likely as the cyclone
encounters the less favorable environment.  Thus Rosa is forecast to
continue to gradually weaken until it approaches Baja California as
a tropical storm.  The intensity guidance is in good agreement on
this scenario, and the new NHC prediction is basically an update of
the previous one after accounting for the initial winds.

Rosa has turned to the north-northwest and accelerated, with an
initial motion of 340/8.  The cyclone should turn to the north
tomorrow and move faster to the north-northeast on Sunday ahead of a
mid- to upper-level trough approaching the west coast of the United
States.  There are no substantial guidance changes to consider, and
with the model consensus being quite reliable so far, it makes
sense to stay near that aid, which is also very close to the
previous forecast.

Key Messages:

1. The main hazard expected from Rosa or its remnants is very heavy
rainfall in Baja California, northwestern Mexico and the 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. Rosa could also bring tropical storm conditions to portions of
the central and northern Baja California peninsula in a few days.
Interests in those locations should monitor the progress of Rosa.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 18.4N 118.0W   95 KT 110 MPH
 12H  29/1200Z 19.5N 118.4W   85 KT 100 MPH
 24H  30/0000Z 21.4N 118.8W   75 KT  85 MPH
 36H  30/1200Z 23.3N 118.6W   65 KT  75 MPH
 48H  01/0000Z 25.1N 117.9W   55 KT  65 MPH
 72H  02/0000Z 28.9N 116.1W   40 KT  45 MPH
 96H  03/0000Z 36.0N 112.0W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  04/0000Z...DISSIPATED

$$
Forecaster Blake

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