The heat wave also caused power outages for people in Los Angeles County.
The Los Angeles Department of Water and Power reported at least 6,500 customers were without power in the Metro and San Fernando Valley areas, as well as more than 2,200 in the Hollywood Hills.
By 10:30 p.m., LADWP also reported that Griffith Park and Los Feliz had about 1,900 people without power. Some areas got power again shortly before 11 p.m.
Crews were working to restore electricity to the areas, but did not have estimated restoration times.
The moisture first moved into the Inland Empire, bringing sudden and heavy rains, lightning strikes, winds and thunder.
The storms then moved into Los Angeles County, with reports of rain in Hollywood, Santa Monica, Castaic, Santa Clarita and other areas.
An electrical storm reported in the Santa Monica area prompted the closure and evacuation of all ocean and beach areas. It was unclear when they would be reopened.
Near Castaic, the northbound 5 Freeway was shut down for some time as firefighters battled a 30-acre brush fire along the roadway. The fire was said to be caused by a lightning strike.
In Santa Clarita, a fire destroyed at least 10 cars at College of the Canyons. That fire may have also been caused by a lightning strike.
Flash flood warnings were issued for San Bernardino and Riverside counties, and Riverside County also had a severe thunderstorm warning.
A lightning strike caused a massive power outage in Colton, leaving at least 50,000 people without power in the heat.
In Corona, the area was hit with heavy rains, hail, strong winds and thunderstorms.
The National Weather Service in San Diego tweeted out a photo of a line of power poles down on Corydon Street in Wildomar.
Monsoonal moisture had moved into the state, triggering the thunderstorms and lightning.
Forecasts showed high pressure causing the heat to be almost stationary, meaning the severe weather conditions will stick around for some time.
The risk of storms could increase if Tropical Storm Lidia, south of Baja California, sends more monsoonal moisture into the state.
The Associated Press contributed to this report.