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Hurricane Rosa Discussion Number  23
NWS National Hurricane Center Miami FL       EP202018
200 PM PDT Sun Sep 30 2018
 
An Air Force Reserve Unit Hurricane Hunter aircraft recently
investigated Rosa, and found peak 700-mb flight-level winds that
still supported minimal hurricane intensity.  However, the
SFMR-observed surface winds were somewhat lower, which is not
surprising since the system has minimal deep convection and is over
24-25 deg SSTs.  Given that the central pressure is still fairly
low, 982 mb, Rosa is being maintained, perhaps generously, as a
hurricane for this advisory.  With increasing shear and cooler
waters ahead for the system, weakening seems inevitable.  The
official intensity forecast is similar to the latest HWRF model
prediction, and shows Rosa weakening to a depression by the time it
reaches the southwest United States.
 
The initial motion is north-northeastward, or 025/10 kt.  The track
forecast scenario remains essentially unchanged from the previous
couple of advisory packages.  The flow on the eastern side of a
large mid-level trough approaching from the west should steer Rosa
on a north-northeastward track for the next couple of days.  The
official track forecast is very close to the latest dynamical model
consensus.
 
The wind radii have been adjusted slightly based on data from a
recent ASCAT scatterometer overpass.
 
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  30/2100Z 25.2N 118.1W   65 KT  75 MPH
 12H  01/0600Z 26.5N 117.4W   55 KT  65 MPH
 24H  01/1800Z 28.1N 116.2W   45 KT  50 MPH
 36H  02/0600Z 29.9N 115.0W   40 KT  45 MPH...INLAND
 48H  02/1800Z 32.3N 113.9W   30 KT  35 MPH...INLAND
 72H  03/1800Z 37.0N 112.0W   20 KT  25 MPH...POST-TROP/INLAND
 96H  04/1800Z...DISSIPATED
 
$$
Forecaster Pasch
 
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