Hurricane Dolores was a powerful tropical cyclone, whose remnants produced a 1-in-500 year event in Riverside County, California. The seventh named-storm, fourth hurricane, and third major hurricane of the record-breaking 2015 Pacific hurricane season, Dolores formed from a tropical wave that crossed into the Northeastern Pacific tropical cyclone basin from Central America on July 8. The wave spawned an area of low pressure, which organized into a tropical depression at 12:00 Coordinated Universal Time (UTC) on July 11. The cyclone strengthened into a tropical storm six hours later, receiving the name Dolores from the National Hurricane Center (NHC). At 12:00 UTC on July 13, Dolores became a Category 1 hurricane. The cyclone subsequently underwent a period of rapid intensification, finally peaking as a Category 4 hurricane, with maximum 1-minute sustained winds of 130 mph (215 km/h) and a minimum central pressure of 946 mbar (27.9 inHg), at 06:00 UTC on July 15. An eyewall replacement cycle and cooler sea-surface temperatures weakened Dolores rapidly, and the storm fell to tropical storm intensity just two days later. At 18:00 UTC on July 18, Dolores degenerated into a remnant low west of the Baja California Peninsula. The remnants drifted northward, towards California, before turning southwestward and dissipating on July 21.
The proximity of Dolores to Mexico led to tropical storm watches being issued for parts of the coastline. Those were later discontinued as Dolores began tracking westward away from land areas. Mexican authorities advised people to take precautions and issued alerts. Hurricane conditions were reported on Socorro Island, an island in the open Pacific owned by Mexico. In Jalisco and Cólima, heavy rainfall was reported, with a few rockslides and minor damage. Further north, a large flash flood affected the city of Tijuana. Over 300 structures were damaged and destroyed, and cars and furniture were swept away.
Dolores produced large waves up to 10 ft (3.0 m) high and dangerous rip currents, drowning a swimmer in Zuma Beach in California. There were many occurrences of flash flooding and severe weather associated with the remnants of Dolores in California and the Southwestern United States. Heavy rain totaling up to 4 in (100 mm) in San Diego and Los Angeles counties broke historic records. Precipitation measurement tools estimated up to 10.6 in (270 mm) of rainfall fell in some areas of California. The Los Angeles Angels experienced their first rain out since 1995. Many highways, including Interstates 5, 8, 10, 15, 80, 215, and 805 were closed due to flooding, mudslides, and severe weather. A bridge on Interstate 10 in Riverside County was washed out, injuring a driver and forcing the closure of both the eastbound and westbound lanes. More than 2,000 lightning strikes were recorded in San Diego County, sparking bushfires and causing a tree to fall on a home. A man was killed by a lightning strike in Kern County, and another man was injured by lightning in San Bernardino County. In Arizona, flash flooding damaged many buildings and roads in Wickenburg. A total of 36 power poles were brought down in Mohave County, and hurricane-force wind gusts were recorded. Similar occurrences were observed in Nevada. Total damage from the hurricane was estimated at US$ 51.136 million.
Meteorological history
The possibility of tropical cyclogenesis from a tropical disturbance south of Mexico was first mentioned by the NHC on July 6, 2015. A tropical wave, which is an area of relatively low atmospheric pressure that spans from east to west in the tropics, crossed Central America and entered the Eastern Pacific Ocean on July 8. The next day, the wave spawned a weak area of low pressure while south of Guatemala. On July 10, the disturbance quickly organized, with convection, or thunderstorms, becoming more concentrated near the center of the low. This was due to an interaction with a strong upper-level trough to the west of the wave. Although the trough moved away from the tropical wave later that day, strong upper-level divergence maintained convection. Early on July 11, satellite images showed that the disturbance was consolidating into a tropical depression, and at 12:00 UTC, the NHC designated the system as Tropical Depression Five-E while located roughly 345 mi (555 km) south-southeast of Acapulco, Mexico. The system's development and tropical cyclogenesis was enhanced by external forces from the upper-level trough; this type of tropical cyclogenesis was quite rare in the Eastern Pacific Ocean. The depression gradually organized, developing banding features around the eastern portion of the system. Late that day, a small central dense overcast developed near the low-level circulation center. A ship near northeastern quadrant of the storm reported sustained winds of 40 mph (64 km/h), and an Advanced Scatterometer pass indicated 49 mph (79 km/h) winds; the depression was upgraded to a tropical storm and received the name Dolores based on this data.
Despite nearly-ideal environmental conditions that were largely favorable for strengthening, moderate northwesterly wind shear caused by a upper-level trough initially prevented much intensification. The storm slowly strengthened on July 11 while moving northwestward, several hundred miles off the coast of Southwestern Mexico. The cloud pattern of the storm grew more and more organized throughout July 12, with symmetric and organized convection over the center, signalling less impediment from the shear, though outflow remained restricted over the western portion of the system. Dolores attained hurricane status at 12:00 UTC on July 13, as it turned westward away from the Mexican coastline, with a ragged eye developing alongside more convective banding. As wind shear northwest of the storm began relaxing, spiraling bands began developing over the western portion of the storm's center. Dolores continued to gradually organize and intensify, though dry air entrainments briefly halted intensification. However, soon afterward, at 00:00 UTC on July 15, Dolores rapidly intensified into a Category 2 hurricane, with the eye becoming more apparent on satellite imagery and very cold cloud tops developing near the center of circulation. Six hours later, Dolores peaked as a Category 4 hurricane with winds of 130 mph (215 km/h) and a minimum pressure of 946 mbar (hPa; 27.94 inHg). Dolores became the earliest occurrence of the third Category 4 hurricane recorded of a Pacific hurricane season, surpassing Hurricane Frank, which attained Category 4 status on July 17, 1992.
The strengthening trend was short-lived, however, as the cloud tops in the eyewall began to warm soon after it achieved peak intensity. As Dolores approached Socorro Island, the cyclone underwent an eyewall replacement cycle and began to steadily weaken. The storm exhibited winds of 105 mph (170 km/h) as it passed within 20 mi (32 km) of the island. After completing the cycle on July 16, Dolores exhibited annular characteristics, with a symmetric structure and wide eye. The NHC described the eyewall as thick and "donut-shaped". Cloud tops briefly cooled, which usually signals the redevelopment of strong thunderstorms, but dry air had begun to mix into the circulation. Around this time, Dolores reached cooler sea surface temperatures, resulting in slow but continuous weakening. Throughout the early hours of July 17, Dolores's structure continued to decay, with an eye no longer apparent on visible satellite imagery and convection waning. The continued effects of cool sea-surface temperatures, abetted by strong wind shear, decoupled the low- and mid-level circulation centers on July 18. Around this time, the rapidly weakening cyclone accelerated north-northwestward between a subtropical ridge to the east and a trough offshore California. By 12:00 UTC that day, Dolores had deteriorated into a tropical storm, with no convection near its center. The system eventually degenerated into a post-tropical remnant low about 300 mi (480 km) west of the Baja California coast at 18:00 UTC on July 18.
From July 18 to 19, the remnants stalled southwest of San Diego, causing its moisture to be carried northward. Initially, only light rain was forecast for California. However, dew points rose to around 70 °F (21 °C), and atmospheric instability was greater than expected. As a result, severe thunderstorms with heavy rain formed. The rainstorms that Dolores had caused were blamed on the slow movement of the storm, as well as enhanced moisture from the record-breaking 2014–2016 El Niño event, which was the same phenomenon that caused the above-average 2015 Pacific hurricane season. The remnant low slowly curved southward, before dissipating on July 22, a few hundred miles west of San Diego, California. Christopher Landsea, a meteorologist at the NHC, noted that the strong subtropical ridge present in typical Pacific hurricane seasons during July was quite weak in 2015. The ridge, normally stationed over Mexico, would drive tropical cyclones westward, but the weakness allowed Dolores to become one of the northernmost traveling tropical cyclones on record in the Northeast Pacific basin in July.
Preparations and impact
Mexico
Due to the threat of tropical storm-force winds reaching the coast, Tropical Storm Watches were issued by the Government of Mexico for parts of the southwestern coast of the country, from Lázaro Cárdenas to Cabo Corrientes. These watches were discontinued on July 13, when Dolores pulled out to sea. The Mexican National Service also warned of hailstorms and waves of 4 to 5 m (13 to 16 ft). The agency ordered mariners, along with tourists and people engaging in recreational activities, to take "extreme caution" due to storm surge. The weather service also advised residents to be attentive to the statements issued by authorities and the National Civil Protection System after rainfall in association with Dolores and other weather systems was forecast to affect the entire country. Oswaldo Hernández Arvizu, director of the Civil Protection Element in Jalisco, warned of landslides and recommended people to drive with increased caution. In Baja California State, authorities ordered drivers to reduce their speed by 10 percent. Residents living on slopes or areas prone to landslides were advised to carry out a review of their soil and house conditions.
As the eye of Dolores passed just northeast of Socorro Island, an automated weather station on the island recorded sustained hurricane-force winds. The station reported 1-minute sustained winds of 79 mph (128 km/h), with a wind gust of 115 mph (185 km/h). Although the center of Dolores stayed away from mainland Mexico, the proximity of the storm to the country’s southwestern coast allowed rainbands to affect several states. The National Weather Service of Mexico noted that the impact from the rainbands extended to Chiapas, Oaxaca, Morelos, Mexico, Michoacán, Colima, Jalisco, Nayarit, Sinaloa, and Baja California Sur, along with Mexico City. The rainbands occasionally caused heavy rain. Patrolling units from the Civil Protection System in Jalisco removed stones that had fallen onto roads. After the storm, roads in the state were passable. In Baja California State, Dolores dropped heavy rain. The Seguridad Pública del Estado (Secretariat of Public Safety of the State) reported 171 emergency calls, including 140 from the city of Tijuana. On July 19, around 1.5 in (38 mm) of rainfall overwhelmed the city’s drainage system, causing mass flash flooding and property damage. Within 15 minutes, a mudslide damaged at least 300 homes and businesses. News and media reports described the mudslide as an "avalanche". Household items were washed into the streets, and vehicles were swept away. In communities such as Fidel Velasquez and Fraccionamiento El Refugio, floodwaters reached 5.9 ft (1.8 m) high. Around 40 families were evacuated.
In the aftermath of the flooding, researchers at the Department of Urban and Environmental Studies of the Colegio de la Frontera Norte (College of the Northern Frontier) deemed that Tijuana was not prepared to face a rain level similar to the one on July 19. The director of Civil Protection in Baja California, Antonio Rosquillas Navarro, stated that the storm infrastructure is "not worthy of the city". The Secretary of Urban Development in Tijuana blamed the floods on garbage in the streets obstructing the storm drains, preventing them from working at full potential. Media reports partially attributed this to the rapid population growth in Tijuana.
United States
As a tropical cyclone, Dolores caused rip currents along beaches in Southern California, which claimed the life of one person. Rainfall and thunderstorms were not reported prior to the hurricane becoming post-tropical. A surge of moisture associated with the remnants of the cyclone moved northward, ahead of a trough off the California coast, between July 17 and 18. The interaction of the moisture with the trough caused an outbreak of severe weather and heavy rainfall across California, Arizona, and Nevada. On July 19, the Weather Prediction Center (WPC) issued a slight risk of flash flooding in its Excessive Rainfall Outlook for the western half of Arizona, and parts of California and Utah. The risk was expanded to include much of Southern California and southeastern tip of Nevada later that day. On July 20, the WPC modified the risk, confining it to mainly Southern California. The National Climatic Data Center estimated overall damage in the country to exceed $51.1 million.
California
Waves of up to 10 ft (3.0 m) were forecast for portions of Southern California, including Huntington Beach Pier in Huntington Beach. Prior to the storm, officials prepared for high waves and rip currents. Newport Beach increased the number of active lifeguards. The National Oceanic and Atmospheric Administration issued warnings discouraging people from going into the water. The Los Angeles County Fire Department Lifeguard Division monitored reports from the National Weather Service, and surfing was prohibited. On the weekend of July 12 to 13, Los Angeles County reported 270 rescues, including 78 at Zuma Beach, where a 28-year-old man drowned from rip currents on July 13.