SAN DIEGO — Thunderstorms have developed over the mountains in San Diego County Monday, producing moderate to heavy rainfall for another afternoon.

Satellite radar picked up a strong cell in North County east of Palomar Mountain and Highway 79 around 1 p.m. Thunderstorms in the region have brought one to two inches of rain in the warned area and prompted a Flash Flood Warning there until 3:45 p.m. 

For the rest of the San Diego County mountains and deserts, a high influx of moisture has triggered a Flood (Areal) Watch until 10 p.m. Monday night. Excessive runoff may flood low-lying streets, rivers and creeks in areas such as Julian, Pine Valley and Borrego Springs. Strong heating will likely encourage more thunderstorm development over mountains/deserts into the evening.

Thunderstorm activity will subside by Tuesday and Wednesday thanks to the strengthening high pressure over the region, but the drying pattern won’t last long. Monsoonal flow is expected to increase by the end of the work week into the weekend, bringing with it another round of thunderstorms for mountains, deserts and possibly inland valleys.

A shallow marine layer along our coast will bring low clouds and patchy fog later in the evening and Tuesday morning. The marine layer paired with higher humidity will keep daytime highs right near the average for early August or slightly cooler.

The other warning to watch out for is elevated surf for our beaches. Remnants of Tropical Storm Frank is sending a strong south swell to our coast for the next few days, producing dangerous rip currents and big waves (4-7 feet). These conditions will last until Wednesday afternoon with the biggest impact to Orange County beaches.