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Hurricane Hilary Discussion Number  10
NWS National Hurricane Center Miami FL       EP092023
300 PM MDT Fri Aug 18 2023
 
Hilary remains a large and powerful major hurricane.  The Air Force 
Hurricane Hunters sampled the northern portion of Hilary and found a 
higher minimum pressure than expected of 948 mb, 700 mb flight-level 
winds of 113 kt, and peak SFMR surface winds of 93 kt. However, the 
aircraft did not sample the southern half of the circulation, which 
currently has some of the deepest convection. Blending the available 
aircraft data and latest satellite intensity estimates yields an 
initial intensity of 115 kt.
 
Hilary continues to slowly bend to the right, and the initial motion 
is northwestward or 315/10 kt.  A general north-northwest to north 
motion with a steady increase in forward speed is expected tonight 
and through the weekend as the system is steered by pronounced 
steering flow between a strong subtropical ridge over the 
south-central U.S. and a mid- to upper-level low off the central 
California coast.  The models have trended faster this cycle, and 
the NHC forecast has followed suit.  Based on the latest forecast, 
the core of Hilary is expected to be very near the central portion 
of Baja California Saturday night and move inland over southern 
California by Sunday night. It should be noted that strong winds and 
heavy rains will occur well ahead of the center.
 
Fluctuations in the hurricane's strength are expected through 
tonight, but Hilary is expected to begin weakening on Saturday as it 
moves over progressively cooler SSTs and into an environment of 
increasing shear and drier air.  The NHC intensity forecast is lower 
than the previous one, partially due to the lower initial intensity, 
and a little higher than the HCCA and IVCN models.
 
 
KEY MESSAGES:
 
1. Heavy rainfall associated with Hilary will begin well in advance 
of the center, from the Baja California Peninsula into the 
Southwestern United States. Preparations for the impacts of flooding 
from rainfall should be completed as soon as possible, as heavy rain 
will increase ahead of the center on Saturday. In the Southwestern 
United States, flash, urban, and arroyo flooding is expected, with 
the potential for dangerous and locally catastrophic impacts.
 
2. Hurricane conditions are expected within portions of the
hurricane warning area along the west-central coast of the Baja
California Peninsula Saturday night and are possible in the
Hurricane Watch area.
 
3. Tropical storm conditions are possible by late Sunday in 
portions of southern California where a Tropical Storm Watch is in 
effect.
 
4. Large swells generated by Hilary will affect portions of the 
coast of southwestern Mexico, the Baja California peninsula, and
south California over the next few days. These swells are likely
to cause life-threatening surf and rip current conditions.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/2100Z 18.7N 112.2W  115 KT 130 MPH
 12H  19/0600Z 20.3N 113.2W  115 KT 130 MPH
 24H  19/1800Z 22.6N 114.1W  105 KT 120 MPH
 36H  20/0600Z 25.6N 115.0W   85 KT 100 MPH
 48H  20/1800Z 29.4N 116.1W   65 KT  75 MPH
 60H  21/0600Z 34.1N 117.3W   45 KT  50 MPH...INLAND
 72H  21/1800Z 39.3N 117.7W   30 KT  35 MPH...POST-TROP/INLAND
 96H  22/1800Z...DISSIPATED
 
$$
Forecaster Cangialosi
 
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