A surge of monsoonal moisture is expected to bring thunderstorms and heavy rain to San Diego County Thursday, which could lead to flash flooding in the mountains and deserts and lightning strikes along the coast.
A National Weather Service flash flood watch for the mountains and deserts is scheduled to remain in effect through Thursday evening, as will a beach hazards statement warning of possible lightning, elevated surf and strong rip currents.
Heavy rain and isolated thunderstorms are expected to develop over the mountains and deserts Thursday morning as an upper level disturbance moves through the region. Forecasters said slower moving thunderstorms would follow and will likely stick around into the early evening hours.
"Daytime heating with decreasing cloud cover should lead to thunderstorms developing in the mountains and deserts during late morning and afternoon hours, and also in the Inland Empire," according to the weather service.
Meteorologists said recently burned areas would be particularly susceptible to flash flooding and debris flows.
The threat of thunderstorms and flash floods is expected to diminish by late evening, according to the weather service.
On Wednesday, the monsoonal atmosphere out of Baja California brought lightning and downpours to eastern San Diego County. The electrical storm struck southeast of Alpine about 5 p.m., and meteorologists logged 13 lightning strikes within an hour, according to the weather service.
Forecasters said similarly unsettled conditions would be likely through the remainder of the workweek, which would be followed by a spell of decreasing humidity and diminishing thunderheads over the weekend.
The storms could also wreak havoc along the beaches. Lightning, strong rip currents and higher than average surf are expected.
"A weak upper level low pressure system moving across the area overnight along with increasing humidity will increase the chances of thunderstorms and dangerous cloud to beach/water lightning," according to the weather service. "A long period southwest swell will continue to create conditions favorable for large and strong rip currents and elevated surf."
Surf of up to 4 feet with sets to 5 feet will be possible through Thursday evening, along with potentially dangerous rip currents.
"Strong rip currents and elevated surf will result in very dangerous swimming conditions," forecasters said. "Swimmers in shallow water may unexpectedly get pulled out by the rip currents or the larger breaking waves."
Rip currents are typically stronger and more frequent around jetties, inlets and piers. Forecasters said swimmers should know how to escape a rip current by swimming parallel to the coast before heading back to shore.
