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Hurricane Hilary Discussion Number  13
NWS National Hurricane Center Miami FL       EP092023
900 AM MDT Sat Aug 19 2023
 
Although Hilary continues to maintain a well-defined circular eye,
the convective pattern has become increasingly asymmetric during the
past several hours.  Deep convection has been eroding on the
system's west side as dry and stable air has been wrapping into
that portion of the circulation.  A blend of the latest satellite
intensity estimates supports nudging the initial intensity downward
to 110 kt for this advisory.  The Air Force Hurricane Hunters are
scheduled to investigate the system later today, and the data they
collect will provide a better assessment of Hilary's intensity and
structure.

The major hurricane continues to turn to the right, and the latest 
initial motion is north-northwestward, or 345/14 kt.  The steering 
currents are well established and consist of a strong mid-level high 
pressure area over the south-central U.S. and a mid- to upper-level 
low off the central California coast.  The flow between these 
features should cause Hilary to accelerate to the north-northwest or 
north during the next day or two, with the core of the system 
reaching the central portion of the Baja California Peninsula 
tonight and southern California Sunday afternoon or evening.  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 will also begin well in advance of the 
arrival of the center.

Hilary is expected to weaken quickly while it moves northward due to 
significantly cooler waters, drier air, and an increase in vertical 
wind shear.  Even though weakening is anticipated, Hilary is still 
expected to be a hurricane when it moves near or over the central 
portion of the Baja California peninsula, but is expected to decay 
to a tropical storm before it moves over southern California. The 
intensity models are in good agreement, and the NHC forecast is 
near the middle of the guidance envelope.


KEY MESSAGES:
 
1. Preparations for flooding impacts should be completed as soon as 
possible, as heavy rainfall will begin well in advance of the 
center. In the Southwestern U.S., 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 late 
tonight 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 afternoon 
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.
 
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  19/1500Z 22.3N 113.5W  110 KT 125 MPH
 12H  20/0000Z 24.6N 114.1W   90 KT 105 MPH
 24H  20/1200Z 28.3N 115.2W   70 KT  80 MPH
 36H  21/0000Z 33.4N 116.7W   50 KT  60 MPH...INLAND
 48H  21/1200Z 39.6N 117.4W   30 KT  35 MPH...POST-TROP/INLAND
 60H  22/0000Z...DISSIPATED
 
$$
Forecaster Cangialosi
 
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