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Hurricane Hilary Discussion Number   6
NWS National Hurricane Center Miami FL       EP092023
300 PM MDT Thu Aug 17 2023
 
Hilary has an impressive appearance on satellite imagery.  The
eye, which is becoming better defined, is surrounded by very cold
cloud tops in the CDO.  There are numerous convective banding
features, especially over the eastern semicircle of the
circulation.  Upper-level outflow is well-defined over all but the
northwestern quadrant of the circulation.  Recent objective Dvorak
T-numbers support an intensity of about 95 kt, which is used for
this advisory.
 
The hurricane continues to move on a west-northwestward track with
an initial motion estimate of 300/13 kt.  Global models indicate
that a mid-tropospheric ridge currently situated to the north of
Hilary will shift eastward over the next few days while a cutoff
low remains near the California coast.  This should result in a
steering pattern that will cause the system to gradually turn
toward the northwest, north-northwest, and north with increasing
forward speed during the next 72 hours.  The official forecast
track has not changed much from the past few advisory packages, and
is a blend of the simple and corrected dynamical model consensus
solutions.  Since the forecast track is roughly paralleling the
coastline north of the central Baja peninsula to the California
border, it nearly impossible to know at this point if the
center will remain just offshore or move over the peninsula before
reaching the southwestern United States.
 
Hilary is over very warm waters, near 30 deg C, with extremely
low vertical wind shear and a moist mid- to low-level atmospheric
environment.  Therefore additional intensification is highly
likely for the next day or so.  The various SHIPS rapid
intensification (RI) indices continue to show high probabilities of
RI during the next day or so.  The most likely indicated intensity
increase is around 25 kt over the next 24 hours, which is also shown
in the NHC forecast.  Later in the forecast period, cooler waters
and land interaction should result in some weakening.  The official
wind speed forecast remain near or above latest HCCA guidance.  The
surface circulation is likely to be dissipated by day 5, but a day 5
forecast point (as a remnant low) is still provided to maintain a
forecast track over the southwestern United States.
 
 
KEY MESSAGES:
 
1. Heavy rainfall associated with Hilary may produce areas of flash
flooding and result in landslides over portions of Baja California
Peninsula from late Friday 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
possible 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 and
hurricane watches could be issued for a portion of that area
tonight.  Tropical storm conditions are expected to spread across
the southern portion of the Baja California Peninsula by late Friday
where a Tropical Storm Warning is in effect.
 
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 on Friday.
 
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  17/2100Z 16.1N 108.9W   95 KT 110 MPH
 12H  18/0600Z 17.0N 110.4W  110 KT 125 MPH
 24H  18/1800Z 18.4N 112.0W  120 KT 140 MPH
 36H  19/0600Z 20.3N 113.0W  120 KT 140 MPH
 48H  19/1800Z 22.4N 113.8W  115 KT 130 MPH
 60H  20/0600Z 25.0N 114.5W  105 KT 120 MPH
 72H  20/1800Z 28.5N 115.4W   85 KT 100 MPH
 96H  21/1800Z 35.4N 118.4W   30 KT  35 MPH...INLAND
120H  22/1800Z 43.0N 120.0W   20 KT  25 MPH...POST-TROP/INLAND
 
$$
Forecaster Pasch
 
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