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Tropical Storm Hilary Discussion Number  18
NWS National Hurricane Center Miami FL       EP092023
200 PM PDT Sun Aug 20 2023
 
Hilary made landfall over the northern Baja California Peninsula a
few hours ago with maximum winds estimated to be around 55 kt.
Since then the storm has continued to move north-northwestward with
the center now nearing the California/Mexico border.  Maximum
sustained winds are now estimated to be near 50 kt based on the
earlier aircraft data and satellite estimates.  Surface
observations indicate that tropical-storm-force winds have spread
into southern California and there have been a few reports of gusts
around hurricane force.  In addition, radar images show that bands
of heavy rain have spread across portions of the southwestern United
States and this will continue through early Monday.
 
The storm is moving quickly to the north-northwest, with the latest
initial motion estimated to be 345/20 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.
Little change was made to the previous track forecast.
 
Continued weakening due to dry air, and land interaction is 
expected, but Hilary is forecast to remain a tropical storm while it 
moves over southern California through tonight. 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 to continue across the
northern portion of the Baja California Peninsula within the
Tropical Storm Warning area during the next few hours.
 
3. Tropical storm conditions are expected in portions of the
southwestern U.S. within the Tropical Storm Warning
area through tonight.  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 so. These swells are likely to cause life-threatening
surf and rip current conditions.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  20/2100Z 31.3N 116.1W   50 KT  60 MPH
 12H  21/0600Z 35.8N 117.2W   35 KT  40 MPH
 24H  21/1800Z 41.8N 117.3W   25 KT  30 MPH...POST-TROP/INLAND
 36H  22/0600Z...DISSIPATED
 
$$
Forecaster Cangialosi
 
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