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Hurricane Hilary Discussion Number  15
NWS National Hurricane Center Miami FL       EP092023
900 PM MDT Sat Aug 19 2023
 
Hilary's cloud pattern has continued to gradually decay this
evening.  The eye is no longer discernible and the convective cloud
tops have warmed near the center.  However, there are plenty of
curved bands around the circulation, and these continue to spread
well northward into the Baja California Peninsula. Subjective and
objective satellite intensity estimates have continued to decrease
and the initial intensity has been reduced to 80 kt. Another Air
Force Reserve reconnaissance mission is schedule overnight which
should provide better information about the structure and intensity
of the cyclone.
 
The initial motion estimate is north-northwestward or 345/15 kt.
The flow between a strong mid-level ridge over the south-central
United States and a mid- to upper-level low over off the central
coast of California will steer Hilary north-northwestward at an
increasingly faster pace during the next 12 to 24 hours.  This will
bring the center of Hilary near the west-central coast of the Baja
California peninsula late tonight or early Sunday and into southern
California by late Sunday afternoon.  The NHC track forecast is
again very similar to the previous advisory and lies near the
middle of the tightly clustered guidance envelope.  Users are
reminded that the exact details of the track forecast, including
where Hilary might make landfall, are of little overall importance
since strong winds and heavy rainfall will extend far from the
center.  These hazards are already spreading northward over the
Baja California Peninsula well in advance of the arrival of the
center.
 
Cooler waters, drier air, and increasing vertical wind will continue
to cause a decrease in intensity as Hillary moves northward.
However, the cyclone is expected to still be a hurricane when it
moves near or over the west-central coast of the Baja California
Peninsula overnight, and confidence remains high that Hilary will 
move into southern California as a tropical storm. 
 
 
KEY MESSAGES:
 
1. Preparations for flooding impacts associated with Hilary should
be completed as soon as possible, as heavy rainfall will begin well
in advance of the center. In the Southwestern United States, the
potentially historic amount of rainfall is expected to cause flash,
urban, and arroyo flooding including landslides, mudslides, and
debris flows. Dangerous to locally catastrophic flooding impacts are
expected early Sunday through early Monday.
 
2. Hurricane conditions are expected along the west-central coast of
the Baja California Peninsula within the hurricane warning area
tonight and Sunday morning, and are possible in the Hurricane Watch
area on Sunday.
 
3. Tropical storm conditions are expected to begin Sunday 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
couple of days. These swells are likely to cause life-threatening
surf and rip current conditions.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  20/0300Z 25.3N 114.6W   80 KT  90 MPH
 12H  20/1200Z 28.3N 115.4W   65 KT  75 MPH
 24H  21/0000Z 33.6N 117.2W   45 KT  50 MPH...INLAND
 36H  21/1200Z 39.5N 118.3W   30 KT  35 MPH...POST-TROP/INLAND
 48H  22/0000Z...DISSIPATED
 
$$
Forecaster Brown
 
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