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Hurricane Hilary Discussion Number   5
NWS National Hurricane Center Miami FL       EP092023
900 AM MDT Thu Aug 17 2023
 
Hilary has continued to intensify rapidly.  The cloud pattern of 
this large hurricane is very impressive, with extremely intense 
deep convection and cloud tops to -80 deg C or colder.  
Well-defined banding features are evident over all quadrants of the 
circulation. The upper-level outflow pattern is quite symmetric and 
expanding.  Satellite intensity estimates are wide-ranging and 
the Dvorak technique rules do not allow subjective current 
intensity estimates much above 65-70 kt.  However based on data 
T-numbers the advisory intensity is set, perhaps conservatively, to 
75 kt. 
 
The hurricane is moving west-northwestward, or about 300/12 kt.  
Over the next few days, a mid-level ridge to the north of Hilary 
is forecast to shift eastward while a mid-level low remains near 
the California coast.  This evolution of the steering currents 
should result in a gradual turn toward the north in a couple of 
days, which would bring Hilary near the Baja California peninsula 
in 72 hours or so and near the U.S./California border in 3-4 days.  
The official forecast track is very similar to the previous one, 
and follows the HFIP corrected consensus, HCCA, guidance.  Although 
there is fairly high confidence in the track prediction, Hilary's 
oblique angle of approach to the west coast of the Baja California 
peninsula makes 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 in an environment of low shear and high mid- to low-level 
humidity, and over very warm waters.  The SHIPS rapid 
intensification (RI) indices show extremely high probabilities of 
rapid intensification during the next day or so.  Therefore the 
official intensity forecast shows a 40-kt increase over the next 24 
hours.  Later in the forecast period, cooler waters and land 
interaction should result in some weakening.  The official wind 
speed forecast is near or a little above the 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 southern California.
 
 
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. Hilary has the potential to bring significant impacts to the
Baja California Peninsula and portions of the southwestern United
States this weekend and early next week, including after it becomes
post-tropical.  Although it is too soon to determine the location
and magnitude of wind impacts, interests in these areas should
monitor the progress of Hilary and updates to the forecast.  
Tropical Storm Warnings and Watches are now in effect for 
southern portions of Baja California Sur, and additional watches or 
warnings will likely be required later today.
 
3. Large swells from Hilary will spread northward along the coast
of southwestern Mexico and the Baja California Peninsula during the
next several days.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/1500Z 15.5N 107.8W   75 KT  85 MPH
 12H  18/0000Z 16.4N 109.4W  100 KT 115 MPH
 24H  18/1200Z 17.6N 111.2W  115 KT 130 MPH
 36H  19/0000Z 19.3N 112.7W  120 KT 140 MPH
 48H  19/1200Z 21.2N 113.7W  115 KT 130 MPH
 60H  20/0000Z 23.6N 114.4W  105 KT 120 MPH
 72H  20/1200Z 26.6N 115.0W   85 KT 100 MPH
 96H  21/1200Z 33.4N 116.8W   50 KT  60 MPH...INLAND
120H  22/1200Z 41.0N 119.0W   25 KT  30 MPH...POST-TROP/INLAND
 
$$
Forecaster Pasch
 
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