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Hurricane Hilary Discussion Number   8
NWS National Hurricane Center Miami FL       EP092023
300 AM MDT Fri Aug 18 2023
 
Hilary's satellite presentation has continued to improve overnight,
with a solid ring of cold cloud tops surrounding a warming eye.
TAFB and SAB provided consensus Dvorak estimates of T6.0/115 kt
while objective estimates are a bit higher, between 125-135 kt.
The advisory intensity is therefore set at 125 kt as a blend
of the various estimates.  Hilary has rapidly intensified by a
remarkable 65 kt over the past 24 hours.  The hurricane remains
large, and the initial wind radii have been adjusted based on a
recent ASCAT-C pass.  An Air Force Reserve Hurricane Hunter
aircraft is scheduled to investigate Hilary around midday and
should provide a more precise estimate of the hurricane's intensity.
 
The hurricane continues to move toward the west-northwest, or 300/11
kt.  However, with mid-tropospheric high pressure nudging eastward
from the Rocky Mountains into the Central Plains, and a cut-off low
off the California coast, Hilary is expected to turn northwestward
very soon and then turn northward and begin accelerating by 48
hours.  The track guidance is more tightly clustered than usual
during the first 72 hours of the forecast, and therefore there is
relatively high confidence in the NHC track forecast, which is
essentially unchanged from the previous advisory.  Since Hilary's
forecast track parallels the coast from the central Baja California
peninsula northward to southern California, it is still nearly
impossible to predict an exact landfall location, not to mention
that Hilary's exact landfall probably won't make much difference
when it comes to the expected hazards and impacts in the region.
 
Hilary could strengthen a little more during the next 12 hours or
so.  However, once hurricanes reach major hurricane strength, they
are prone to fluctuations in intensity, particularly if an eyewall
replacement begins.  In addition, oceanic heat content will be
dropping significantly in 24-36 hours, and it's likely that Hilary's
large wind field will mix up cooler water ahead of the arrival of
the center.  This colder water, as well as potential interaction
with the terrain of the Baja California peninsula, is expected to
induce faster weakening over the weekend, with Hilary likely to drop
below hurricane intensity some time on Sunday.  Due to its
accelerating motion in 2 to 3 days, Hilary is still expected to be
producing tropical-storm-force winds when it reaches southern
California.  The surface circulation is likely to dissipate soon
after moving into California, but a day 4 remnant low point is still
shown over the western U.S. for continuity purposes.
 
 
KEY MESSAGES:
 
1. Heavy rainfall associated with Hilary may produce areas of flash
flooding and result in landslides over portions of the Baja
California Peninsula from late today into late Sunday.  Rainfall
impacts from Hilary within the Southwestern United States are
expected to peak this weekend into Monday. Flash, urban, and arroyo
flooding is expected with the potential for significant impacts.
 
2. The threat of hurricane-force wind impacts is increasing along
the west-central coast of the Baja California Peninsula, where a
hurricane watch is in effect.  Tropical storm conditions are
expected to begin across the southern portion of the Baja California
Peninsula later today and then spread northward through the weekend.
 
3. The threat of significant wind impacts continues to increase for
the northern portions of the Baja California Peninsula and the
Southwestern United States, especially in areas of mountainous
terrain.  Although it is too soon to determine the location and
magnitude of these impacts, interests in these areas should monitor
the progress of Hilary and updates to the forecast.  Watches could
be issued for portions of this area, including along the southern
California coast, later today.
 
4. Large swells from Hilary will spread northward along the coast
of southwestern Mexico and the Baja California Peninsula.  These
swells will reach the Gulf of California and northern portions of
the Baja California Peninsula later this weekend.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0900Z 17.2N 110.8W  125 KT 145 MPH
 12H  18/1800Z 18.3N 112.0W  130 KT 150 MPH
 24H  19/0600Z 20.2N 113.2W  120 KT 140 MPH
 36H  19/1800Z 22.4N 114.0W  105 KT 120 MPH
 48H  20/0600Z 25.3N 114.7W   85 KT 100 MPH
 60H  20/1800Z 28.7N 115.6W   65 KT  75 MPH
 72H  21/0600Z 32.9N 116.7W   50 KT  60 MPH...INLAND
 96H  22/0600Z 43.6N 117.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  23/0600Z...DISSIPATED
 
$$
Forecaster Berg
 
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