In Mexico, the hurricane's threat caused thousands of people to evacuate to shelters and for ports to close along the coast. In anticipation of "catastrophic and life-threatening flooding", the
National Hurricane Center (NHC) issued its first-ever
tropical storm warning for
Southern California, extending from the
Mexico–United States border to just north of
Los Angeles.[1] Persistent heavy rainfall, potentially "more than a year’s worth of rain" in some areas, was forecasted. Due to this, flood watches were issued, affecting about 26 million people across four states (
Arizona, California,
Nevada, and
Utah), and the region was placed under a high risk threat for flash flooding by the
Weather Prediction Center (WPC).[2][3][4]
In Mexico, the hurricane killed two people due to floodwaters, and left 250 million
pesos (US$14.7 million) in damage. The storm left behind flooded roads, mudslides and downed trees in the Baja California peninsula and in Southern California. Some areas of the latter region received up to 600% of their annual rainfall averages for the month of August.[5] The floods killed one person in
San Bernardino County, California. Damage in the United States were estimated at US$900 million, much of it in
Inyo County, California, where most of the roads in
Death Valley National Park were damaged by floods. The park was closed for two months, its longest ever closure. Hilary broke records in four U.S. states for
wettest tropical cyclone or its remnants.
Meteorological history
The
origins of Hilary was from a
tropical wave that exited the western coast of
Africa around August 3. The wave moved westward across the
Atlantic Ocean, reaching the
Lesser Antilles by August 9. On that day, the
National Hurricane Center (NHC) first identified the potential for the eventual development, 156 hours before Hilary's formation.[6] The tropical wave crossed
Central America into the far eastern
Pacific Ocean on August 12, producing a large area of disorganized
convection, or thunderstorms.[6][7] As early as August 13,
hurricane prediction models anticipated a tropical cyclone would affect Mexico and the southwestern United States.[8] A
low pressure area developed on August 14 south of the
Gulf of Tehuantepec, as the thunderstorms gradually organized. After a
low-level circulation formed early on August 16, the system developed into a tropical depression by 06:00
UTC, located about 345 mi (555 km) south of
Acapulco. Six hours later, the depression intensified into a tropical storm, and the NHC
named it Hilary.[6]
Upon its formation, Hilary was moving northwestward, steered by a
ridge over Mexico. Atmospheric and environmental conditions were conducive for further strengthening, including warm
sea surface temperatures of near 30 °C (86 °F), ample moisture, and low
wind shear.[6] Accordingly, the NHC warned that Hilary had a high likelihood of
rapid intensification.[9] Convection around the storm increased and organized into a
central dense overcast, with an
eye developing in the center.[10] On August 17, Hilary intensified into a hurricane, by which time it had expanded into a large tropical cyclone, with tropical storm-force winds extending 230 mi (370 km) from the center.[6] Symmetric
outflow and pronounced
rainbands developed around the hurricane.[11] Early on August 18, Hilary intensified into a Category 3 hurricane on the
Saffir-Simpson scale, thus becoming a major hurricane.[6] The convection around the center organized into a thick ring around the eye.[12] At 06:00 UTC that day, the NHC estimated that Hilary attained a peak intensity of 140 mph (220 km/h), making it a Category 4 hurricane, while its
barometric pressure dropped to 940 mbar (28 inHg). The intensity estimate was based on satellite imagery using the
Dvorak technique. By the time of its peak, Hilary commenced a 48 hour period of intensification following its development.[6]
After reaching its peak intensity, Hilary weakened slightly due to an
eyewall replacement cycle, in which the inner eye collapsed as the larger, outer eyewall contracted.[6] The
Hurricane Hunters first investigated the storm late on August 18, by which time Hilary fell to Category 3 intensity. Around that time, the hurricane began moving more to the northwest, reaching the western periphery of the ridge over Mexico.[13][6] Another Hurricane Hunters flight on August 19 observed that Hilary re-intensified into a Category 4 hurricane, with a secondary peak of 130 mph (215 km/h), and a pressure of 943 mbar (27.8 inHg). Thereafter, drier and stable air began affecting the hurricane, along with cooler water temperatures, causing the eye to fall apart. Hilary quickly weakened as it accelerated north-northward, responding to the steering influences of a
trough of low pressure near the California coast and a ridge of high pressure over the central United States. The hurricane weakened into a tropical storm on August 20, as wind shear from the trough displaced the thunderstorms far north of the center. At around 17:00 UTC that day, Hilary made
landfall in a sparsely-populated region of northwestern Mexico in the state of
Baja California, with sustained winds estimated at 60 mph (95 km/h).[6] This was about 215 mi (345 km) south-southeast of
San Diego,
California.[14]
After moving ashore, Hilary's circulation became elongated and disrupted over the mountainous terrain of Baja California. Devoid of convection, Hilary degenerated into a
post-tropical cyclone, and soon after was absorbed by a low pressure area developing near the southern coast of California, outside of Hilary's wind radius. Operationally, NHC had tracked the two systems as the same, assessing that Hilary continued into southern California as a tropical storm,[6] which would have had made it the first tropical storm to cross into the state since
Nora in 1997.[15] The combined system, which included the remnants of Hilary continued moving through the western United States, eventually crossing into Canada.[16][17]
Preparations
Mexico
The
Mexican government issued watches for southern Baja California Sur on August 17.[18] They were upgraded to warnings later that day.[19] Hurricane watches were issued for western parts of the Baja California peninsula at 03:00 UTC on August 18, and by 15:00 UTC the same day, they were upgraded to hurricane warnings as hurricane watches were issued for the west coast of
Baja California.[20]
Nearly 1,900 people in Mexico evacuated to shelters along the Baja California peninsula. This included about 850 people evacuated by the Mexican Navy from five offshore islands.[21] Several schools in
Cabo San Lucas were used as temporary shelters, and 18,000 soldiers were on alert.[22] Officials closed ports from
Oaxaca to
Colima on August 17,[23][24] and later extended closures to Baja California Sur. School classes and public activities were cancelled in Baja California, with a baseball game postponed.[25] Around 20 flights were cancelled at
Los Cabos International Airport.[26] Beaches were closed in
La Paz,
Tijuana, and
Ensenada.[22][27][28]
United States
On August 15, five days before Hilary's landfall and a day before the system was named, local
National Weather Service (NWS) offices in California first released videos and briefings related to the potential impacts. The first issued a
flood watch on August 17 for the mountain and desert regions of southern California.[8] A day later, the NHC issued its first-ever
tropical storm watch for
Southern California, later upgraded to a tropical storm warning.[29][30] The
Weather Prediction Center (WPC) also issued a level 4/high risk for excessive rainfall, which was the first ever high risk of flash flooding in the desert valleys of Southern California east of the
Peninsular Ranges.[29][31] The NWS issued a flood watch for portions of California,
Nevada,
Utah, and
Arizona, affecting about 26 million people.[4] WPC forecaster David Roth described the rainfall potential as "exceedingly rare, bordering on unique, for the region from a tropical cyclone and unique for Nevada, which had its first ever High Risk WPC Day issued for the state". Roth expected a broad area would experience 1-in-100 year rainfall totals.[32][33][34] The NWS also issued flash flood warnings for San Bernardino and Kern counties.[35]
On August 20, the
Storm Prediction Center issued a level 2/slight risk in Southern California, which included 5% risk of tornadoes.[36] That night, a tornado warning was issued for
Alpine and
Descanso in
San Diego County.[37] The WPC later forecast the chance for 5 inches (130 mm) of rainfall in the mountains of Idaho from the system.[38]Federal Emergency Management Agency (FEMA) staff and personnel were ordered to be positioned in southern California by President
Joe Biden, and Biden urged residents and people in the storm's path to take precautions.[39][40][41] An
emergency operations center was opened in San Diego and Los Angeles.[42][43][44]
Hurricane Hilary caused three fatalities in Mexico during its passage, all related to vehicles swept away by floodwaters. One occurred in
Santa Rosalía in Baja California Sur, when floodwaters breached a protection wall, sweeping away a vehicle, with four of the occupants rescued. The other fatalities occurred in
Cataviña in Baja California and in
Navolato in Sinaloa.[6][85] From its genesis to its dissipation, Hilary's outer rainbands affected much of western Mexico as far southeast as
Oaxaca.[86] Offshore western Mexico, Hurricane Hilary passed west
Socorro Island near the time of its peak intensity, producing wind gusts of 79 mph (128 mph). Along the Baja California peninsula, Hilary produced heavy rainfall and gusty winds. The heaviest rainfall was 12.83 inches (326 mm), recorded in San Lucas Norte in northeastern
Baja California Sur, which was 180% of the average annual rainfall for the state. High rains caused flooding and landslides across the peninsula. Rainfall spread across the peninsula and into the adjacent states of
Sonora and
Sinaloa. The highest wind gust in Mexico was recorded by a high-altitude
anemometer in
Sierra de la Laguna, which recorded wind gusts of 99 mph (159 km/h) at an elevation of 6,395 ft (1,949 m). Closer to sea level, wind gusts reached 69 mph (111 km/h) at
Loreto International Airport along the peninsula's eastern coast. Tropical storm-force winds extended into the state of
Sonora, where
Mar de Cortés International Airport recorded gusts of 66 mph (105 km/h).[6]
The state government of Baja California Sur estimated
Mex$250 million (US$14.5 million) worth of damage, related to Hilary. At least 87 homes were damaged in the state, with the worst damage in
Loreto,
Mulegé, and
Comondú.[6] Torrential rainfall caused widespread flooding and landslides in Baja California Sur.[26] Officials in Baja California reported numerous mud and rock slides across the state along with several power outages.[87] In
Los Cabos at the southern end of the peninsula, the hurricane caused minor damage to utilities and roads, including potholes.[88] In the state of Baja California, floods damaged the
Transpeninsular Highway, as well as a dozen major roads.[6] Coastal areas of
Sinaloa recorded torrential rains from the hurricane's passage.[89] In Sinaloa, the storm knocked down 33 power poles, affecting rural roads.[85]
United States
The remnants of Hilary moved through the western United States, producing rainfall from California as far north as Montana. The maximum recorded precipitation of 13.07 in (332 mm) at Upper Mission Creek in southeastern California.[16] Damage nationwide was estimated at US$900 million.[6] The system's push toward Southern California coincided with a 5.1 magnitude earthquake that struck north of Los Angeles near
Ojai, California, along with numerous aftershocks. Only minor damage and no injuries were reported from the quakes.[90][91] As a result, the term "hurriquake" trended on social media.[92][93]
California
While Hilary approached and dissipated near Southern California, the storm produced locally high winds along with heavy rainfall, with some desert locations receiving more than half of their annual rainfall in a single day.[8] The strongest gusts were recorded in Los Angeles County – 87 mph (140 km/h) at
Magic Mountain, and San Diego County – 84 mph (135 km/h) at
Big Black Mountain.[94] High winds knocked down at least 50 power poles in the town of
Thermal.[95] The highest rain totals were recorded in the
San Bernardino Mountains – 11.73 in (298 mm) at Raywood Flats, and the
San Jacinto Mountains – 11.74 in (298 mm) at
Mount San Jacinto.[94] Floodwaters in the community of Angelus Oaks swept away a mobile home, killing a woman.[6] The remnants of Hilary set rainfall records across the state.[6] Rainfall at
Furnace Creek in
Death Valley totaled 2.20 in (56 mm), setting a new single-day rainfall record; the amount was more than the annual average rainfall of 2.15 in (55 mm).[96] On August 20, downtown Los Angeles and San Diego each recorded its wettest single summer day on record (June through August) with 2.48 in (63 mm) and 1.82 in (46 mm) of precipitation, respectively.
Palm Springs recorded 3.18 in (81 mm), also a single summer day record amount,[97] or 69% of its average annual rainfall.[8] Along the coast, Hilary caused beach erosion.[6]
The collective impacts of downed trees and floods damaged or washed away roads in 13 counties across California, from
San Diego and
Imperial counties along the state's southern border with Mexico to
Siskiyou County in far northern California. The
California Department of Transportation (CALTRANS) estimated the cost to repair roads at over $146 million.[35] Portions of
I-5,
I-8, I-10,
I-15, the
Pacific Coast Highway, and other roads closed.[48][49][98][99] A nearly 30 mi (48 km) stretch of
Interstate 10 (I-10) closed for two days from the floods, mud, and debris, which stranded hundreds of vehicles, and made it difficult to travel to Palm Springs.[100][101] Near Twentynine Palms, high winds blew the roof of a building.[6] In Imperial County near
Ocotillo, I-8 was closed for two days after three large boulders fell onto the eastbound highway.[102][6] On the same interstate, the high winds blew over two semi-trucks.[103] Closed
state roads included portions of routes
14,
38,
58,
127,
136,
178, and
190.[35][104] In Death Valley National Park, flash floods damaged all of the nearly 1,400 mi (2,300 km) of roads, forcing the park to close for two months. Near
Lone Pine, floodwaters from the Lone Pine Creek destroyed portions of Whitney Portal Road, which provides access to
Mount Whitney. Damage in Inyo County alone was estimated at $500 million.[105][106][104][107][108] Flash floods also damaged roads and trails in Mojave National Preserve.[109] Farther north, heavy rain produced mudslides and flash flooding in Siskiyou County near
Mount Shasta, damaging roads and rains.[110]
Damage in Riverside County totaled $126 million, including about $83 million in damaged roads and bridges, and about $26 million affecting water systems.[111] That made it the costliest natural disaster in the history of the county, with much of it occurring in the
Coachella Valley.[112] Across the valley,
9-1-1 phone service was down for a few days, which required residents to either text or call alternate numbers for emergencies.[95][100] At least six state highways in Riverside County were closed due to floods, debris flow, or rockslides.[95] Floods washed out a bridge over the Mias Canyon, isolating residents in
Oak Glen.[113] In
Seven Oaks, around 30 people required rescue after the
Santa Ana River overflowed, with several homes and vehicles destroyed.[6] Along the
Whitewater River, floodwaters 15 ft (4.6 m) deep damaged a bridge, derailed eight train cars, and buried another train in mud.[114][115] In Palm Desert, floodwaters displaced at least 30 residents in the Spanish Walk neighborhood.[116][117] Also in Palm Desert, high winds knocked down a large tree, blocking a portion of
SR 111.[118] In
Cathedral City, floodwaters entered a nursing home, requiring 14 people to be rescued by
loaders.[119] At least 10 people in Thermal evacuated to shelters.[120] Floodwaters entered
Eisenhower Medical Center in
Rancho Mirage, but this did not impact operations there.[47] In Palm Springs, the floods inundated vehicles,[47] while downed power lines sparked a few small fires.[100]
In San Diego, the heavy rainfall caused the
San Diego River to quickly rise to a crest of 9.6 ft (2.9 m).[121] City firefighters rescued a group of 13 people from a flooded homeless camp along the river, while the Harbor Police rescued two people from a boat washed against
Harbor Island.[122] Floodwaters washed out a portion of
SR 78 at
Yaqui Pass.[123] High winds overturned a
semi-trailer truck near
Borrego Springs.[124] In
La Habra in Orange County, the winds damaged housing shingles.[125] About 41,000 customers were left without electricity across the Los Angeles area. Also in the city, a mudslide damaged the
Marlton School.[126] Across the
Imperial Valley, high winds downed trees and power poles, as well as damaging a gas station canopy in
El Centro.[57] Damage in Imperial County reached $9.3 million.[101] In
Barstow, a lightning strike knocked down a power pole onto I-15, closing the highway.[127] The storm spawned a
microburst in Fresno, producing winds of 55 mph (89 km/h), which knocked down 50 trees at the Belmont Country Club. Winds also knocked down a power pole and electric lines in the city.[128][129][130]
Elsewhere
New U.S. wettest tropical cyclones and their remnants records[nb 2]
Locally heavy rainfall spread across much of the western United States from the remnants of Hilary.[16] Arizona received much less precipitation from Hilary than forecasted, only peaking at (2.10 in (53 mm) in
Hilltop.[131][94] However, records for wettest (total rainfall) tropical cyclones and their remnants were broken in four states:
Idaho,
Montana, Nevada, and
Oregon.[17] The strongest winds beyond California primarily occurred in Nevada and Utah at high-elevation locations above 9,000 ft (2,700 m). In a mountainous area near
Mount Charleston, in
Clark County, Nevada, wind gusts reached 82 mph (132 km/h), strong enough to knock down a few trees.[132] The weather station at
Cardiff Pass in Utah recorded a gust of 75 mph (121 km/h).[94] Thunderstorms produced high winds near
Weiser, Idaho, reaching 69 mph (111 km/h), strong enough to knock down a few trees.[133][134]
The new peak rainfall in Nevada was more than double the previous record, with 9.20 in (234 mm) recorded in
Lee Canyon.[17][94] Across
Spring Mountains National Recreation Area and nearby mountainous areas, the rains produced flash flooding, which washed away roads, underground pipes, a fire station, and trails. The damage, estimated at $25 million, closed the recreation area until October 26, when
Nevada State Route 156 (Lee Canyon Road) was reopened.[135][136][137] The community of
Mount Charleston had to
shelter in place after electricity and road access were cut off. The town's fire department was inundated with mud, with houses and a nearby school damaged. A landslide also damaged part of Lee Canyon Ski and Snowboard Resort.[6] Floods closed a portion of
U.S. Route 95 in
Nye County, Nevada.[138] The rains rose the water levels in
Lake Mead by 0.16 in (4.1 mm).[113] In eastern
Washington, rain from the system was beneficial with helping extinguish the
2023 Washington wildfires.[139]
Aftermath
Due to storm damage, Riverside County announced in September 2023 the availability of tax relief for property owners incurring more than $10,000 in damage, while also opening an office in Yucaipa to provide assistance to the public. On October 3, the United States
Small Business Administration opened a Disaster Loan Outreach Center in Angelus Oaks, to provide loans to homes and businesses affected by the storm.[112][140] On October 5, the U.S. Department of Transportation’s
Federal Highway Administration announced the release of $15.3 million in emergency funds to help rebuild roads and bridges in 12 California counties.[141] On November 22, U.S. President Joe Biden announced a major disaster declaration for five California counties affected by the storm: Imperial, Inyo, Kern, Riverside and Siskiyou. The announcement provided federal funding for emergency work toward repairing or replacing damaged public facilities.[142] On December 14, the Palm Desert city council authorized a $4.63 million contract to expand a water retention basin by about 36%, near where I-10 was flooded. The project was intended to withstand the 100 year flood.[116] In the Mount Charleston region of Nevada, workers spent $11 million to reopen roads to the mountainous communities.[143] At the Lee Canyon Ski Resort, workers used dump trucks to restore damaged ski slopes,[144] reopening the resort on November 4.[145]
In Death Valley National Park, workers began clearing and assessing the damaged roads and infrastructure after the rains ended. Late on August 21, crews reopened state route CA-190 to allow an exit for those who stayed in the park during the floods; however, the road was not opened fully until October 15, marking the longest ever closure in the park's history.[146][147] The
Federal Highway Administration's Emergency Relief for Federally Owned Roads program funded the road repairs, which continued over the following months. On November 1, the park's entrance in
Beatty, Nevada re-opened with emergency repairs.[107][148] Following heavy rainfall in Death Valley, floodwaters reformed the ancient
Lake Manly in what the usually dry
Badwater Basin, lasting several months.[149] The road to Badwater Basin reopened on November 20, allowing access to the temporary lake.[150] Following additional rainfall from
an atmospheric river in February 2024, the park allowed visitors to kayak on the temporary lake, which grew to a length of 6 mi (9.7 km), a width of 3 mi (4.8 km), and a depth of 1 ft (0.30 m).[151]
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