A thunderstorm and flash flooding was reported near Borrego Springs on Monday, and showers were developing elsewhere in San Diego County.
Strong rip currents and elevated surf persist along the coast.
About 9 a.m., National Weather Service radar showed flash flooding from a thunderstorm 10 miles northwest of Borrego Springs, moving northeast about 5 mph. The rain was falling between 1.5 and 2 inches of rain per hour, and forecasters said the runoff was headed for Borrego Springs.
The weather service issued a flash flood warning for the northeastern reaches of the county, including Borrego Springs, that was originally set to expire at noon. It has been extended until 2 p.m.
A flash flood watch will extend through Monday evening for the mountains and deserts. About 8:15 a.m., showers were developing east of Warner Springs and north of Ranchita.
Thunderstorms are expected in the mountains through early Monday afternoon. Rain is possible in the deserts Monday afternoon and evening, according to the National Weather Service.
"Given the high moisture content of the atmosphere and slow movement of storms, there is a high potential for heavy rainfall and flash flooding from thunderstorms this afternoon, especially along the east slopes of the mountains and adjacent desert areas," according to the weather service.
The risk of flash flooding will be the greatest in steep canyons, downstream from mountains and in areas recently denuded by wildfire, where runoff and debris can clog washes, forecasters said. Flash flooding can develop miles away from the storm and turn normally dry creek beds into raging torrents.
A beach hazards statement is in effect through Monday night for the county's coastal areas, where the surf is running at 4-6 feet, with sets of up to 8 feet — thanks to tropical storm Norbert. Coastal flooding is possible at high tide.
"The elevated surf and large tidal swings will mean strong rip and long shore currents at area beaches," according to the weather service. "Swell and surf will decrease late tonight."
The currents could result in dangerous swimming conditions, especially for those with little experience in the water, according to the weather service. Beachgoers were advised to obey posted warning signs, use caution in and around the water and to swim near a lifeguard.
