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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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