Authorities have issued a flash flood watch for inland areas of southwest California.
City News Service said the National Weather Service forecasts a chance of strong thunderstorms late Saturday afternoon and evening in both mountain and desert regions.
Affected areas encompass San Diego, Riverside and San Bernardino counties.
Forecaster Mike Webster says monsoonal moisture originating off the coast of Mexico is causing extremely humid conditions which could feed slow-moving thunderstorms with heavy amounts of rainfall.
Webster says monsoonal weather conditions are likely to continue through the next couple weeks.
The weather service says foothills and recently burned slopes are particularly vulnerable to debris slides. Motorists should not attempt to drive in storm conditions.
A fast-moving storm caused some flooding in the area Friday afternoon, but little damage was reported.