Tropical Storm Hilary brought record heavy rainfall to parts of Southern California, triggering flooding and mudslides which shut down major roads and forced multiple high-water rescues.

Screenshot from Palm Springs Police Department drone footage of flooding and storm damage on Gene Autry Trail, California, after heavy rain from Tropical Storm Hilary. Photo: Palm Springs Police Department

Hilary previously caused severe flooding in parts of western Mexico as a category 1 hurricane, before weakening and moving into California as a Tropical Storm on 20 August. Hilary is the first tropical storm to hit Southern California in 84 years. The governor of California declared an emergency in advance of the oncoming storm on 19 August.

According to the National Weather Service Los Angeles, rainfall on 21 August 2023 broke several long-standing records. Among others, the weather stations in Downtown Los Angeles recorded its wettest ever August day, with 2.48 inches / 62.992 mm. The previous high was 2.06 inches / 52.324 mm set on 17 August 1977.

Mount Wilson in Los Angeles County recorded 8.56 inches / 217.42 mm of rain in 48 hours to 21 August. The weather station in Mount San Jacinto, Riverside County, recorded 11.74 inches / 298.2 mm during the same period.

Teams from police, firefighters and the California National Guard responded to incidents caused by flooding and mudslides across areas of Riverside, Los Angeles, Ventura and San Bernardino counties.

Areas around the desert resort city of Palm Springs and nearby Cathedral City in Riverside County were among the hardest hit. Over 40 people were recued from floods in Cathedral City. Floods washed out several roads around Palm Springs including parts of Interstate 10 which was closed for a period. Palm Springs City Government declared a local emergency.

California National Guard’s 330th Military Police Company supported Cathedral City and Palm Springs fire departments during rescue operations. Photo: California National Guard

In San Diego County, firefighters rescued 9 people from the riverbed in the area of the Morena Boulevard Bridge in San Diego City. No injuries were reported but the Fire Department said crews were still looking for more people who may need help.

In San Bernardino, firefighters were assisting around 800 people after floods and mudslides in Oak Glen, Forest Falls, Angelus and Seven Oaks. Around 30 people were rescued in Seven Oaks, where the Santa Ana River overflowed.