Showers developed Thursday over much of Southern California, including downpours in the High Desert and San Bernardino County mountains, ahead of flash flood warnings that went into effect for a widespread part of the region.
Flash flood warnings are in effect Thursday afternoon for parts of San Bernardino, Ventura, Los Angeles and Riverside counties.
Beaumont, Hemet and other Inland Empire communities reported some of the heaviest showers at noon Thursday. Thunder and lightning also were reported in the Santa Clarita Valley north of Los Angeles.
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A flash flood watch includes the Colby fire burn area in the San Gabriel Valley foothills. Rainfall rates might reach 1 to 2 inches per hour or more, possibly causing mud a rock slides in the area east of Los Angeles that burned in January 2014.
Roads might be closed due to flooding, according to Azusa police.
Hot and humid weather that has descended on the region brings the threat of thunderstorms and flooding at least through Friday. Isolated thunderstorms and sometimes-heavy rain are forecast to continue into early next week.
Unlike the storm system two weeks ago resulting from remnants of Hurricane Dolores, which dumped rain across Southern California, the latest weather system is driven by moisture coming from the Gulf of Mexico and will mostly affect only the mountains and deserts.
In those areas, there will be a chance of thunderstorms every day through early next week, with the potential for heavy precipitation in some places.
Dangerous rip currents are expected along the Southern California coast.
On Tuesday, more than 400 rescues were reported off the California coast. There were about 66 rescues at Northern beaches, 103 rescues at central beaches, and 235 rescues in the South Bay area, according to Los Angeles County Fire Department.
On Wednesday, four people were rescued off Venice Beach.