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Hurricane Hilary Discussion Number  11
NWS National Hurricane Center Miami FL       EP092023
900 PM MDT Fri Aug 18 2023

Hilary's cloud pattern has not changed much since earlier today.  
The hurricane continues to exhibit a large 30-35 n mi wide eye with 
a surrounding ring of deep convection with clouds tops around -75
degrees Celsius. The latest subjective Dvorak intensity estimates
from TAFB and SAB support an initial intensity of 115 kt. The next
Air Force Reserve reconnaissance mission is currently en route, and
it should provide a better assessment of Hilary's intensity and
structure overnight.
 
Hilary has turned north-northwestward with an initial motion
estimate of 335/12 kt. The track forecast reasoning is unchanged
from before.  Hilary is forecast to turn northward and begin to
accelerate on Saturday as it is steered by deep-layer southerly flow
between a strong subtropical ridge over the south-central United
States and an upper-level low off the coast of central California.
The models have again trended slightly faster, and the NHC foreast
has been adjusted accordingly.  The NHC track forecast brings the
center near the west-central coast of the Baja California Peninsula
in about 36 hours, and along the northwestern coast of the peninsula
in 48 hours.  This is near the middle of the tightly clustered
guidance envelope.  Users are reminded to not focus on the exact
details of the track forecast as strong winds and heavy rainfall 
will extend far from the center.  These hazards will begin well in
advance of the arrival of the center.
 
Hilary has likely peaked in intensity, and weakening is expected to
begin on Saturday as it moves over cooler SSTs.  A faster rate of
weakening is likely to begin by 24 hours as Hilary moves over
SSTs less than 26C and the vertical wind shear begins to increase.
However, Hilary is forecast to be a large hurricane when it passes
near the west-central coast of the Baja Peninsula, and a
tropical storm when it nears the U.S./Mexico border.  The NHC
intensity forecast is similar to the previous advisory, and lies
close to the IVCN consensus model.
 
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
dangerous and locally catastrophic impacts likely.
 
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 expected to begin on Sunday in 
portions of southern California where a Tropical Storm Warning is in 
effect.
 
4. Large swells generated by Hilary will affect portions of the
coast of southwestern Mexico, the Baja California peninsula, and
southern 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  19/0300Z 19.7N 112.7W  115 KT 130 MPH
 12H  19/1200Z 21.4N 113.6W  110 KT 125 MPH
 24H  20/0000Z 24.2N 114.4W   95 KT 110 MPH
 36H  20/1200Z 27.6N 115.4W   80 KT  90 MPH
 48H  21/0000Z 32.1N 116.8W   55 KT  65 MPH...INLAND
 60H  21/1200Z 37.8N 117.8W   30 KT  35 MPH...POST-TROP/INLAND
 72H  22/0000Z...DISSIPATED
 
$$
Forecaster Brown
 
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