The unusual precaution was prompted by a storm that brought heavy rain and hail in the northwestern reaches of San Diego County. Forecasters said it could lead to dangerous lightning strikes near the beaches and flash flooding elsewhere in the county.
A line of thunderstorms moving over south and central San Diego County around 7:30 a.m. upped the risk for cloud-to-ground and cloud-to-water lightning at the beaches, according to the National Weather Service.
A beach hazards statement for lightning, set to remain in effect through 11 a.m., said the thunderstorms and lightning could stick around along the coast until late morning.
“Lightning may cause serious injury or death to those people who are caught on the open coast during a thunderstorm,” according to the weather service advisory.
Forecasters said beaches south of Oceanside were the most susceptible, but thunderstorms could also be possible at beaches in the North County. Beachgoers were advised to move indoors until the storm passes and to avoid metal objects.
The NWS was also advising that the storms could lead to flash flooding elsewhere in the county. A flash flood watch for the mountains, deserts and valleys is set to expire this evening.
“Scattered thunderstorms capable of producing heavy rain will be possible through this evening,” according to the advisory. “Flash flooding is possible where heavy rain occurs and some distance downstream.”
Forecasters said showers and scattered thunderstorms moving across Southern California could lead to more heavy rain and flash flooding, especially along mountain streams, desert washes and below burned areas. The valleys may also be at risk of flooding, especially near the foothills.
Doppler radar indicated moderate to heavy rainfall over burn scars at Camp Pendleton at about 3:20 a.m., according to the National Weather Service. As of about 6:20 a.m., moderate to heavy showers and a few embedded thunderstorms were continuing to move onshore between Oceanside and San Clemente.
An urban and small stream flood advisory for the coastal areas and valleys in the northwestern portion of the county, including Camp Pendleton, Oceanside and Fallbrook, is scheduled to extend until 9:15 a.m.
Forecasters said minor flooding would be possible “due to the continual rain over the recent burn scars in Camp Pendleton.”
“Excessive runoff from heavy rainfall will cause elevated levels on small creeks and streams, and ponding of water in urban areas, highways, streets and underpasses, as well as other poor drainage areas and low-lying spots,” according to the NWS advisory.