Up to several inches of rain fell across the region through the morning and afternoon, much of it in short bursts, according to the National Weather Service.
The deluge left streets, parking lots and garages temporarily underwater and kept emergency crews scrambling from place to place, rescuing motorists trapped in their suddenly submerged vehicles.
Among the many stretches of roadway rendered unsafe or utterly impassible by the downpours over the afternoon were:
-- Alvarado Road and 70th Street in La Mesa;
-- Avenida del Rio, near Fashion Valley mall;
-- Carmel Mountain Road at Sorrento Valley Road in the Torrey Pines area;
-- Carroll Canyon Road and Pacific Heights Boulevard in Sorrento Mesa;
-- Genesee Avenue between North Torrey Pines Road and Interstate 5, near the University of California San Diego;
-- Midway Drive between Rosecrans Street and Sports Arena Boulevard;
-- Mount Aguilar Drive at Mount Alifan Drive in Clairemont Mesa, where firefighters came to the rescue of people stranded in several cars stalled in the intersection;
-- the southbound Interstate 805 off-ramp to Bonita Road;
-- the 2100 block of Monument Road in the Tijuana River Valley;
-- the 10900 block of San Diego Mission Road in Mission Valley; and
-- San Vicente Road at Wildcat Canyon Road in Ramona.
Through the day, emergency personnel responded to numerous other areas where occupied cars wound up stuck in rising floodwaters, said Lee Swanson, a spokesman for the San Diego Fire-Rescue Department. No serious injuries were reported.
At Courtyard San Diego Old Town on Jefferson Street in Old Town, meanwhile, structural flooding caused a roughly 5-by 5-foot piece of drywall to come loose and fall from the ceiling of a flooded reception area about 4 p.m. Several cars also wound up partway underwater in the hotel's inundated underground garage.
A flash-flood watch for the region was slated to remain in effect for the region through late Wednesday night.
The sustained soaking across the county also kept the California Highway Patrol busy. Between midnight and 4 p.m., the agency logged 291 collisions on local freeways and back roads, more than twice the roughly 140 accidents that occur in the area over a typical full day under dry skies.
Over a 24-hour period ending shortly after 5 p.m., the wet clouds dropped 3.01 inches of precipitation at Palomar Observatory; 2.72 at Mount Woodson; 2.46 in Poway; 2.43 at Montgomery Field airport; 2.3 in Kearny Mesa and at Miramar Lake; 2.18 at Henshaw Dam; 2.02 in Mission Valley; 1.97 in San Onofre; 1.77 in Santee; 1.66 at Lindbergh Field; 1.52 in Oak Grove; 1.46 in Point Loma; 1.45 in La Mesa; 1.28 in the Granite Hills area; 1.27 in Carlsbad; 1.24 at Lake Cuyamaca; 1.23 at Otay Mountain; 1.2 in Oceanside; 1.03 in Julian; 0.9 in Encinitas; 0.87 in Warner Springs; 0.63 at Lake Murray; 0.19 in Borrego Springs; and 0.15 in Agua Caliente.
The series of consecutive storms, which is expected to continue into the weekend, likely will bring some local snowfall as well in the East County highlands, possibly beginning late Wednesday, NWS meteorologist Brandt Maxwell said.