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Tropical Storm Hilary Discussion Number  17
NWS National Hurricane Center Miami FL       EP092023
800 AM PDT Sun Aug 20 2023
 
The core of Hilary continues to move quickly north-northwestward
along or just off the west coast of the Baja California Peninsula.
Heavy rains are streaming northward and are now affecting portions
of western Mexico, the northern Baja California Peninsula and the
Southwestern United States.  The satellite appearance of Hilary
continues to degrade as dry and stable air wraps into the
circulation.  The Air Force Hurricane Hunters are investigating
Hilary and found that the pressure has increased to 984 mb and
maximum winds have dropped to near 60 kt, making Hilary a tropical
storm.
 
The storm is accelerating to the north-northwest, with the latest
initial motion estimated to be 345/22 kt.  An even faster motion to
the north-northwest is expected during the next day or so as Hilary
moves in the fast flow between a ridge over the south-central U.S.
and a mid- to upper-level low off the central California coast.
The center of Hilary is forecast to move into southern California
this afternoon and dissipate over the western U.S. on Monday.
 
Continued weakening due to cool waters, dry air, and land
interaction is expected, but Hilary is forecast to remain a
tropical storm before it reaches southern California later today.
The strongest winds are expected to be to the east of the center
and in areas of high terrain.
 
 
KEY MESSAGES:
 
1. Preparations for flooding impacts across the Southwestern United
States should be completed with the peak intensity of heavy rainfall
expected later today through early Monday morning. The potentially
historic amount of rainfall is expected to cause life-threatening to
locally catastrophic flash, urban, and arroyo flooding including
landslides, mudslides, and debris flows through early Monday
morning. Localized flooding impacts, some significant, are also
expected across northern portions of the Intermountain West.
 
2. Tropical storm conditions are expected across the central and
northern portions of the Baja California Peninsula within the
Tropical Storm Warning area through tonight.
 
3. Tropical storm conditions are expected to begin later today in
portions of the southwestern U.S. within the Tropical Storm Warning
area.  Winds could be particularly strong and gusty in and near
areas of higher terrain.  Gusty winds are expected to spread
well inland across the western United States.
 
4. Large swells generated by Hilary will affect portions of the
Baja California Peninsula and southern California over the next
day or two. These swells are likely to cause life-threatening
surf and rip current conditions.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  20/1500Z 29.7N 115.9W   60 KT  70 MPH
 12H  21/0000Z 33.5N 117.0W   45 KT  50 MPH
 24H  21/1200Z 39.9N 118.1W   30 KT  35 MPH...POST-TROP/INLAND
 36H  22/0000Z...DISSIPATED
 
$$
Forecaster Cangialosi
 
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