The National Weather Service has issued a flash flood warning for northern San Diego County and Riverside County through 3:45 p.m. on Monday.
At 12:47 p.m. Doppler radar indicated thunderstorms producing heavy rain across the warned area, which includes Warner Springs in northern San Diego County and Oak Grove, Aguanga and the Cahuilla reservation in Riverside County.
One to 2 inches of rain have already fallen. Additional rainfall amounts of 0.75 to 1.5 inches are possible in the warned area.
Potentially life-threatening flash flooding around creeks and streams, urban areas, highways, streets and underpasses was ongoing or expected to begin shortly after the warning.
The NWS advises residents and travelers to turn around and not drive on flooded roads. Most flood deaths occur in vehicles.
