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Hurricane Hilary Discussion Number   7...Retransmitted
NWS National Hurricane Center Miami FL       EP092023
900 PM MDT Thu Aug 17 2023
 
Hilary continues to rapidly intensify. The presentation on infrared 
satellite imagery has become very impressive, and the hurricane now 
has a thick ring of -70 to -75 C eyewall cloud tops surrounding the 
eye which continues to warm. Earlier AMSR2 and GMI microwave imagery 
showed a similarly impressive structure, with a solid eyewall on 
both 89-GHz and 37-GHz channels. While the most recent subjective 
Dvorak intensity estimates are constrained from increasing as much 
as the satellite presentation would suggest, the objective estimates 
from UW-CIMSS have been rapidly increasing, with the latest 
estimate from ADT at T6.3/122 kt, AiDT at 112 kt, and 107 kt from 
D-PRINT. Hilary's initial intensity will be set at 110 kt for this 
advisory, favoring the objective estimates. 
 
The hurricane has maintained a west-northwestward motion tonight, 
estimated at 300/12 kt. The mid-level ridge currently steering 
Hilary is soon forecast to shift eastward as a mid- to upper-level 
cutoff low swings in from the west and parks itself near the 
central California coast. This pattern should result in Hilary 
starting to turn northwestward and the north-northwestward over the 
next 24-36 hours. A turn more northward should begin by this weekend 
with some gradual acceleration as the hurricane is captured 
downstream of the cutoff low. The track guidance this cycle remains 
tightly clustered, and only slight adjustments to the forecast track 
were made this cycle. This track forecast remains in good agreement 
with the corrected consensus aid (HCCA). Since the forecast track 
continues to be roughly parallel to the coastline north of the 
central Baja peninsula to the California border, it very difficult 
to know if the center will remain just offshore or move over the 
peninsula before reaching the southwestern United States. 

The rapid intensification episode of Hilary is expected to continue 
for at least another 12 hours, and the latest forecast intensity now 
takes the hurricane to 130 kt in that time frame. Afterwards, there 
is an interesting difference between the statistical-dynamical 
models (SHIPS and LGEM) which show a peak intensity in about 24 
hours, and the hurricane-regional models which show a peak a bit 
earlier before gradual weakening begins. While there are few signs 
of an imminent eyewall replacement cycle based on the last few 
microwave passes, it is possible one could occur in another day or 
so. The large 34-kt wind field of the hurricane could also start to 
upwell some cooler waters out ahead of the inner core in 24-36 
hours. Thus, some gradual weakening is now forecast to begin during 
this time period with a faster rate of weakening as the hurricane 
crosses a sharp temperature gradient to the west of the Baja 
Californian peninsula. The official forecast is above the intensity 
guidance in the short-term, but falls back to the consensus aids 
beyond 36 h. The surface circulation is likely to dissipate as it 
pushes far inland in 96 hours, but a point as a remnant low will 
still be shown 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 the 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 the 
government of Mexico has issued a hurricane watch for a portion of 
the west coast of the Baja California peninsula.  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  18/0300Z 16.7N 110.0W  110 KT 125 MPH
 12H  18/1200Z 17.7N 111.4W  130 KT 150 MPH
 24H  19/0000Z 19.4N 112.6W  125 KT 145 MPH
 36H  19/1200Z 21.5N 113.6W  115 KT 130 MPH
 48H  20/0000Z 24.0N 114.3W  100 KT 115 MPH
 60H  20/1200Z 27.2N 115.0W   70 KT  80 MPH
 72H  21/0000Z 30.7N 116.1W   55 KT  65 MPH
 96H  22/0000Z 39.0N 118.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  23/0000Z...DISSIPATED
 
$$
Forecaster Papin
 
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