Hurricane Hilary was a large and intensePacific hurricane in August of 2023 that brought torrential rainfall and gusty winds to thePacific Coast of Mexico ofBaja California Peninsula, and theSouthwestern United States, resulting in widespread flooding and mudslides to the region. The hurricane was the eighthnamed storm, sixth hurricane, and fourthmajor hurricane of the active and highly destructive,2023 Pacific hurricane season.[nb 1] Hilaryoriginated from atropical wave south ofMexico on August 16, and strengthened into a hurricane a day later while paralleling the southwest coast of Mexico. The system underwentrapid intensification, reaching maximum sustained winds of 140 mph (220 km/h) and a central pressure of 940 mbar (27.76 inHg) on August 18, making it a Category 4 on theSaffir-Simpson scale. After environmental conditions became unfavorable, Hilary weakened as it approached land, makinglandfall on August 20 as a tropical storm inSan Quintín along the westernBaja California peninsula. Hilary became a post-tropical cyclone over land, before being absorbed into a new non-tropical low-pressure area early on August 21.
In Mexico, the hurricane killed three people and left at least 854 millionpesos (US$48 million) in damage.[nb 2] Power outages affected 315,929 people in the country, although most service was restored within four days. 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. The floods killed one person inSan Bernardino County, California. The estimated damage total in the United States was US$900 million, much of it inInyo County, California, where most of the roads inDeath 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 forwettest tropical cyclone or its remnants.
Theorigins of Hurricane Hilary were from atropical wave that exited the western coast ofAfrica around August 3. The wave moved westward across theAtlantic Ocean, reaching theLesser Antilles by August 9. On that day, theNational Hurricane Center (NHC) first identified the potential for the eventual development, 156 hours before Hilary's formation.[2] The tropical wave crossedCentral America into the far easternPacific Ocean on August 12, producing a large area of disorganizedconvection, or thunderstorms.[2][3] As early as August 13,hurricane prediction models anticipated a tropical cyclone would affect Mexico and the southwestern United States.[4] Alow-pressure area developed on August 14 south of theGulf of Tehuantepec, as the thunderstorms gradually organized. After alow-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 ofAcapulco. Six hours later, the depression intensified into a tropical storm, and the NHCnamed itHilary.[2]
Upon its formation, Hilary was moving northwestward, steered by aridge over Mexico. Atmospheric and environmental conditions were conducive for further strengthening, including warmsea surface temperatures of near 86 °F (30 °C), ample moisture, and lowwind shear.[2] Accordingly, the NHC warned that Hilary had a high likelihood ofrapid intensification.[5] Convection around the storm increased and organized into acentral dense overcast, with aneye developing in the center.[6] 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.[2] Symmetricoutflow and pronouncedrainbands developed around the hurricane.[7] Early on August 18, Hilary intensified into a Category 3 hurricane on theSaffir-Simpson scale, thus becoming a major hurricane.[2] The convection around the center organized into a thick ring around the eye.[8] 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 itsbarometric pressure dropped to 940 mbar (28 inHg). Operationally, the NHC estimated slightly higher winds of 145 mph (230 km/h), and anticipated some slight further strengthening. The revised intensity estimate was based on satellite imagery using theDvorak technique. By the time of its peak, Hilary had been rapidly intensifying for a continuous 48-hour period following its formation.[2][9]
After reaching its peak intensity, Hilary weakened slightly due to aneyewall replacement cycle, in which the inner eye collapsed as the larger, outer eyewall contracted.[2] TheHurricane 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.[10][2] 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-northwestward, responding to the steering influences of atrough 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 madelandfall in a sparsely populated region of northwestern Mexico in the state ofBaja California, with sustained winds estimated at 60 mph (95 km/h).[2] This was about 215 mi (345 km) south-southeast ofSan Diego,California.[11]
After moving ashore, Hilary's circulation became elongated and disrupted over the mountainous terrain of Baja California. Devoid of convection, Hilary degenerated into apost-tropical cyclone, and early on August 21, it was absorbed by a new non-tropical low-pressure area, which was developing near the southern coast of California outside of Hilary's wind radius. Operationally, the NHC had tracked the two systems as the same, assessing that Hilary continued into southern California as a tropical storm,[2] which would have had made it the first tropical storm to cross into the state sinceNora in 1997.[12] The combined system, which included the remnants of Hilary, continued moving through the western United States and eventually crossed into Canada.[13][14]
TheMexican government first issuedtropical storm watches for southernBaja California Sur on August 17, upgrading them to warnings later that day. 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 ofBaja California.[2]
Nearly 1,900 people evacuated along the Baja California peninsula, utilizing at least 90 shelters. This included about 850 people evacuated by the Mexican Navy from five offshore islands.[15][16] InTijuana, at least 51 people rode out the storm in shelters. Officials in the city also moved homeless people to shelters.[16] In Los Cabos at the southern tip of Baja California, dozens rode out the hurricane in storm shelters.[17] Several schools inCabo San Lucas were used as temporary shelters, and 18,000 soldiers were on alert.[18] Officials closed ports fromOaxaca toColima on August 17,[19][20] and later extended closures to Baja California Sur. School classes and public activities were canceled in Baja California.[21] Around 20 flights were canceled atLos Cabos International Airport.[22] Beaches were closed inLa Paz, Tijuana, andEnsenada.[18][23][24]
On August 15, five days before Hilary's landfall and a day before the system was named, localNational Weather Service (NWS) offices in California first released videos and briefings related to the potential impacts. Two days later, the agency first issued aflood watch on August 17 for the mountain and desert regions of southern California.[4] On August 18, the NHC issued its first-evertropical storm watch forSouthern California, later upgraded to a tropical storm warning.[25][2] TheWeather 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 thePeninsular Ranges.[25][26] The NWS issued a flood watch for portions of California,Nevada,Utah, andArizona, affecting about 26 million people.[27] 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.[28][29][30] The NWS also issued flash flood warnings for San Bernardino and Kern counties.[31]
A mesoscale discussion from the Weather Prediction Center discussing flash flooding expected across most of Southern California as a result of the remnants of Hilary
Hurricane Hilary caused four fatalities in Mexico during its passage, all related to people in vehicles. One occurred inSanta Rosalía in Baja California Sur, when floodwaters breached a protection wall, sweeping away a vehicle, with four of the occupants rescued. There was a traffic accident in Tijuana that led to a death and an injury. InCataviña, Baja California, a driver was swept away by a stream and was killed. The last fatality occurred inNavolato in Sinaloa.[2][84][85][86] From its genesis to its dissipation, Hilary's outer rainbands affected much of western Mexico as far southeast asOaxaca.[87] Offshore western Mexico, Hurricane Hilary passed west ofSocorro 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 northeasternBaja 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 ofSonora andSinaloa. The highest wind gust in Mexico was recorded by a high-altitudeanemometer inSierra de la Laguna, Baja California Sur, 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) atLoreto International Airport along the peninsula's eastern coast. Tropical storm-force winds extended into the state ofSonora, whereMar de Cortés International Airport inPuerto Peñasco recorded gusts of 66 mph (105 km/h).[2]
Across northwestern Mexico, the storm left 315,929 people without electricity.[88] At least 87 homes were damaged in the state, with the worst damage inLoreto,Mulegé, andComondú.[2] Damage in Baja California Sur amounted toMex$427 million (US$24 million).[89] In Santa Rosalía alone, the storm destroyed 26 houses, while inComondú, another 15 buildings were wrecked.[90] In Mulegé municipality, soldiers assisted families in evacuations after a stream flooded houses.[88] Torrential rainfall caused widespread flooding and landslides in Baja California Sur.[22] InLos Cabos at the southern end of the peninsula, the hurricane caused minor damage to utilities and roads, including potholes.[91] Hilary damaged 40 elementary schools, although not to a significant enough degree to disrupt the start of the school year.[92] Officials in Baja California reported numerous mud and rock slides across the state.[93] In the state of Baja California, floods damaged theTranspeninsular Highway and a dozen other major roads.[2] Damage across the state reached Mex$427 million (US$24 million).[89] Coastal areas ofSinaloa recorded torrential rains from the hurricane's passage.[94] In Sinaloa, the storm knocked down 33 power poles, affecting rural roads.[84]
The remnants of Hilary moved through the western United States, producing rainfall from California to as far north as Montana. The maximum recorded precipitation of 13.07 in (332 mm) at Upper Mission Creek in southeastern California.[13] Damage nationwide was estimated at US$900 million.[2] The system's push toward Southern California coincided with a 5.1 magnitude earthquake that struck nearOjai, California, along with numerous aftershocks. Only minor damage and no injuries were reported from the quakes.[105][106] As a result, the term "hurriquake" trended on social media.[107][108] Because Hilary was already weakened by the time of the earthquake, researchers considered it unlikely that the storm triggered the event.[109]
While Hilary approached and dissipated near Southern California, the storm produced locally high winds along with heavy rainfall. Some desert locations receiving more than half of their annual rainfall in a single day, or six times their usual August precipitation.[4][110] The strongest wind gusts were recorded in Los Angeles County – 87 mph (140 km/h) atMagic Mountain. Another hurricane-force wind gust occurred in San Diego County – 84 mph (135 km/h) atBig Black Mountain.[111] High winds knocked down at least 50 power poles in the town ofThermal.[112] The highest rain totals were recorded in theSan Bernardino Mountains – 11.73 in (298 mm) at Raywood Flats, and theSan Jacinto Mountains – 11.74 in (298 mm) atMount San Jacinto.[111] Floodwaters in the community of Angelus Oaks swept away a mobile home, killing a woman.[2] The remnants of Hilary set rainfall records across the state.[2] Rainfall atFurnace Creek inDeath 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).[113] 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,[114] or 69% of its average annual rainfall.[4] Along the coast, Hilary caused beach erosion.[2] The storm's rains caused a temporary break during the2023 California wildfires.[115]
The collective impacts of downed trees and floods damaged or washed away roads in 13 counties across California, fromSan Diego andImperial counties along the state's southern border with Mexico toSiskiyou County in far northern California. TheCalifornia Department of Transportation (CALTRANS) estimated the cost to repair roads at over $146 million.[31] Portions ofinterstates5,8,10, and15 were closed, along with thePacific Coast Highway and other roads.[44][45][116][117] A nearly 30 mi (48 km) stretch of 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.[118][119] In Imperial County nearOcotillo, I-8 was closed for two days after three large boulders fell onto the eastbound highway.[120][2] On the same interstate, the high winds blew over twotractor-trailers.[121] Closedstate roads included portions of routes14,38,58,127,136,178, and190.[31][122] In Death Valley National Park, flash floods damaged all of the 1,323 mi (2,129 km) of roads, including water and sewage lines, with several miles of roads washed away entirely. The resulting damage forced the park to close for two months.[123][124][125][126] NearLone Pine, floodwaters from Lone Pine Creek destroyed portions of Whitney Portal Road, which provides access toMount Whitney.[127] Damage in Inyo County alone was estimated at $500 million.[122] Flash floods also damaged roads and trails in Mojave National Preserve.[128] Farther north, heavy rain produced mudslides and flash flooding in Siskiyou County nearMount Shasta, damaging roads and drains.[129]
Damage in Riverside County totaled $126 million, including about $83 million in damaged roads and bridges, and about $26 million affecting water systems.[130] That made it the costliest natural disaster in the history of the county, with much of it occurring in theCoachella Valley.[131] Across the valley,911 emergency phone service was down for a few days, which required residents to either text or call alternate numbers for emergencies.[112][118] At least six state highways in Riverside County were closed due to floods, debris flow, or rockslides.[112] Floods washed out a bridge over the Mias Canyon, isolating residents inOak Glen.[132] InSeven Oaks, around 30 people required rescue after theSanta Ana River overflowed, with several homes and vehicles destroyed.[2] Along theWhitewater River, floodwaters 15 ft (4.6 m) deep damaged a bridge, derailed eight train cars, and buried another train in mud.[133][134] In Palm Desert, floodwaters displaced at least 30 residents in the Spanish Walk neighborhood.[135][136] Also in Palm Desert, high winds knocked down a large tree, blocking a portion ofSR 111.[137] InCathedral City, floodwaters entered a nursing home, requiring 14 people to be rescued byloaders.[138] At least 10 people in Thermal evacuated to shelters.[139] Floodwaters enteredEisenhower Medical Center inRancho Mirage, but this did not impact operations there.[43] In Palm Springs, the floods inundated vehicles,[43] while downed power lines sparked a few small fires.[118]
In San Diego, the heavy rainfall caused theSan Diego River to quickly rise to a crest of 9.6 ft (2.9 m).[140] 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 againstHarbor Island.[141] Floodwaters washed out a portion ofSR 78 atYaqui Pass.[142] High winds overturned asemi-trailer truck nearBorrego Springs.[143] NearTwentynine Palms, high winds blew the roof of a building.[2] InLa Habra in Orange County, the winds damaged housing shingles.[144] About 41,000 customers were left without electricity across the Los Angeles area. Also in the city, a mudslide damaged theMarlton School.[145] Across theImperial Valley, high winds downed trees and power poles, as well as damaging a gas station canopy inEl Centro.[53] Damage in Imperial County reached $9.3 million.[119] InBarstow, a lightning strike knocked down a power pole onto I-15, closing the highway.[146] The storm spawned amicroburst 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.[147][148][149]
Locally heavy rainfall spread across much of the western United States from the remnants of Hilary.[13] Arizona received much less precipitation from Hilary than forecasted, only peaking at 2.10 in (53 mm) inHilltop.[150][111] However, records for wettest (total rainfall) tropical cyclones and their remnants were broken in four states:Idaho,Montana, Nevada, andOregon.[14] 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 nearMount Charleston, inClark County, Nevada, wind gusts reached 82 mph (132 km/h), strong enough to knock down a few trees.[151] The weather station atCardiff Pass in Utah recorded a gust of 75 mph (121 km/h).[111] Thunderstorms produced high winds nearWeiser, Idaho, reaching 69 mph (111 km/h), which also knocked down trees.[152][153]
The new peak rainfall in Nevada was more than double the previous record, with 9.20 in (234 mm) recorded inLee Canyon.[14][111] AcrossSpring Mountains National Recreation Area and nearby mountainous areas, the rains produced flash flooding, which washed away about 5 mi (8.0 km) worth of roads. The floods also damaged underground pipes, a school, a fire station, and trails. The damage, estimated at $35 million, closed the recreation area until October 26, whenNevada State Route 156 (Lee Canyon Road) was reopened.[154][155][156][157] The community ofMount Charleston had toshelter 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.[2] Floods closed a portion ofU.S. Route 95 inNye County, Nevada.[158] The rains rose the water levels inLake Mead by 4.1 mm (0.16 in).[132] In easternWashington, rain from the system was beneficial with helping extinguish the2023 Washington wildfires.[159] InJackson Hole, Wyoming, the storm brought rain and an uptick inhumidity levels on August 21.[160]
On August 28, 2023, the government of Mexico declared a state of emergency for two municipalities in Baja California –San Quintín andEnsenada – as well as two municipalities in Baja California Sur –Mulegé and Comondú.[161] The state of Baja California Sur utilized emergency funds to mobilize resources toward restoring the damage from Hilary. The Federal Electricity Commission deployed thousands of electricians to restore the damaged power network within four days. Within a day of Hilary's passage, travel resumed along the Transpeninsular Highway, after workers repaired potholes caused by the storm. State officials identified 52 families in high-risk areas to be relocated.[88] By September 5, there were no people remaining in the emergency shelters, as displaced families relocated to hotels.[162]
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 SR 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.[113][163] TheFederal 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 inBeatty, Nevada re-opened with emergency repairs.[126][164] Following heavy rainfall in Death Valley, floodwaters reformed the ancientLake Manly in the usually dryBadwater Basin, lasting several months.[165] The road to Badwater Basin reopened on November 20, allowing access to the temporary lake.[166] Following additional rainfall froman 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 0.30 m (1 ft).[167] By April 2024, the emergency phase in the park had ended after all of the roads were reopened.[123]
Due to the damage in California, 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 StatesSmall Business Administration opened a Disaster Loan Outreach Center in Angelus Oaks, to provide loans to homes and businesses affected by the storm.[131][168] On October 5, the U.S. Department of Transportation’sFederal Highway Administration announced the release of $15.3 million in emergency funds to help rebuild roads and bridges in 12 California counties.[169] On November 22, President 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.[170] 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 the100-year flood.[135] In the Mount Charleston region of Nevada, workers spent $11 million to reopen roads to the mountainous communities.[171] At the Lee Canyon Ski Resort, workers used dump trucks to restore damaged ski slopes,[172] reopening the resort on November 4.[173]
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Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression
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