A flash flood warning was issued Thursday for northwestern and southwestern San Diego County due to heavy rainfall from a powerful storm that was increasing in intensity as the day progressed.

The National Weather Service also elevated a flash flood watch to a flash flood advisory for the entire county due to the heavy downpours. The advisory would be in effect until noon Thursday. Then, the flash flood watch would go into effect until 10 p.m.

The advisory warned that heavy rainfall could trigger flash flooding in low-lying areas or on streets, especially in areas scorched by recent wildfires.

Flash flood warnings were in effect for the area near the San Diego River at Fashion Valley and the area near the Santa Margarita River at San Juan Capistrano due to expected surge as the day progresses.

At 9 a.m., a flash flood warning was issued for the northwestern portion of the county, including Oceanside, Carlsbad, Vista, Encinitas, Poway, Del Mar, Fallbrook, Valley Center, Escondido and Camp Pendleton.

An hour later, the alert was expanded to include southeastern San Diego County. Areas that have the potential for flooding include Chula Vista, El Cajon, La Mesa, Poway, Ramona, Alpine, portions of the San Diego city limits, Mission Valley, Hwy 78 Between Borrego Springs Road and Ocotillo Wells, Cuyamaca Rancho State Park and Borrego Springs.

As traffic picked up Thursday morning, NBC 7 traffic anchor Whitney Southwick tracked flooding on nearly a dozen county roadways.

A Ford Mustang became submerged on Camino Del Rey in the North County where rainfall had flooded a portion of the road in feet-deep water. A North County Fire Protection District ambulance waded through the water to check on the car but no one was in need of rescue, the agency said.

A Cal Fire engine rolled over on a rainy old Highway 395 in Bonsall Thursday morning, though it was still under investigation if wet roadways contributed to the crash that left three firefighters injured.

Also in the North County, the on-ramp from El Camino Real to State Route 78 in was closed due to flooding at the bottom of the ramp. In Fallbrook, flooding was reported at E. Mission Road and N. Brandon Road.

In the East County, flooding at SR-67 and Riverford Road caused a car to slide off the roadway and into a ditch, Southwick said.

The following roadways were closed due to flooding, according to the county Department of Public Works:

16th St between Hwy 67 and H St
De Luz Rd from Royal Glen Dr. to County line
Ramona St., between H St. and Raymond Ave.
De Luz dip is closed from De Luz Murrieta Rd. to County line
De Luz Murrieta Rd. is closed from De Luz Rd. to County line
Camino Del Ray is closed between W, Lilac Road and Old 395
Via Viejas Dip between Calle De Pescadores to Palo Dan Zante
Pala Mission Road between HWY 76 and Pala Temecula Road due to flooding
Little Gopher Canyon Road between Gopher Canyon Road and Old River Road
Old River Road between Dentro De Lomas and Little Gopher Canyon Road
Country Club Dip in the Harmony Grove area
Quarry Rd Dip is between SR125 and Lakeview Ave

The NWS warned drivers to turn around if they come across a flooded roadway.

NBC 7 Meteorologist Sheena Parveen said heavy downpours would move in waves as the storm swept the county.

The above-average rainfall was due in part to a subtropical jet stream that pulls tropical moisture into the region. Combined with the storm system, it creates an atmospheric river, Parveen said.

“This is tropical moisture so you can bet these downpours today, they’re going to be the blinding type. When you’re driving. It’s going to be very hard to see in some instances,” Parveen said.

SeaWorld San Diego was forced to close for the day because of the rain. The park said the safety of their guests was their main priority.

Transportation services were also affected. The North County Transit District (NCTD) said mutliple bus routes were experiencing delays including routes 388, 359, 323, 302, 303, 392,395 and 315.

24-hour rainfall totals through 9 a.m. Thursday were:

San Diego: 0.61”
Bonsall: 3.07”
Fallbrook: 4.03”
Ramona: 1.92”
Santee: 1.44”
Poway: 1.28”
Oceanside: 2.62”
Encinitas: 1.45”
Kearny Mesa: 1.04”
Palomar: 6.76”
Julian: 3.28”
Mt Laguna: 2.47”
Borrego Springs: 0.67”

Showers would begin to taper off at about 6 p.m. Thursday, but chances for rain will last until the weekend, Parveen said.

In total, the storm could bring 2 to 3 inches of rain to the coast and inland valleys; in the mountains 6 inches or more of rain is possible and in the deserts, less than a half-inch is expected.

A high wind warning for the mountains was downgraded early Thursday to an advisory, as wind gusts lowered slightly from 65 miles per hour to 55 mph.

Breezy conditions with winds averaging 25 to 35 mph were still expected in all other parts of the county.

Photo Credit: North County Fire Protection District
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Source: NBC San Diego