New Storms on Horizon : Weather: Flooded freeways and mudslides hamper traffic. Brief respite is expected today.

Heavy rain continued to drench Southern California on Thursday from a storm system that swept away cars in overflowing streams, blocked canyon roads with mudslides, flooded houses and freeways and led to the deaths of at least three people in weather-related traffic accidents.

An 11-year-old boy was rescued from a rain-swollen flood-control channel in Ventura County by three Simi Valley High School students.

For the third time in as many days, the National Weather Service issued urban flood warnings Thursday evening as powerful downpours hammered hillside communities in Los Angeles Orange, Riverside, San Diego and Ventura counties.

Forecasters said the rain should stop this morning and skies should clear briefly this afternoon before clouding up again Saturday with the arrival of a new weather system that is expected to drop more heavy rain over the weekend.

Seasonal rainfall totals were well above normal throughout the Southland. Meteorologists say that a continuing onshore flow of moist, warm air from over the tropical Pacific and more cold fronts heading south from the Gulf of Alaska mean that there could be additional rain for the next week or so.

Between 4 p.m. Wednesday and 4 p.m. Thursday, another 2.21 inches of rain fell at the Los Angeles Civic Center, raising the season’s total to 9.43 inches, compared to a normal season’s total for the date of 5.48 inches. More than 3 1/2 inches of rain had fallen since the stormy weather began late Tuesday night.

Two of the storm-related fatalities occurred when a car skidded on wet pavement and struck two teen-agers walking along the shoulder of Grand Avenue in Walnut, the California Highway Patrol said.

Brien Stewart, 17, and Jeff Heuser, 16, both of Walnut, were pronounced dead at hospitals about an hour after the Wednesday night accident. The car’s driver, a 24-year-old Glendora woman, was not cited.

A man was killed near Los Angeles International Airport early Thursday when his car slid out of control in a pool of water on Pershing Drive, slammed into a light standard and burst into flames. Police said the victim, who was burned beyond recognition, was not immediately identified.

Slides closed portions of Malibu Canyon, Kanan and Triunfo Canyon roads shortly after dark on Thursday, and oozing mud forced the temporary closure of the California Incline, a sloping ramp between Ocean Avenue and the Pacific Coast Highway in Santa Monica.

Water collected by flood control channels in the San Fernando Valley rose behind Sepulveda Dam, forcing the closure of streets running through the flood control basin about 4:30 p.m., Los Angeles police said.

Streets closed included Burbank Boulevard between the Golden State Freeway and Balboa Boulevard, Officer Gary Weller said. Woodley Avenue was shut down between Burbank and Victory boulevards.

Morning and evening commutes were slowed to a crawl as rain squalls reduced visibility, flooded freeway lanes and caused a rash of minor traffic accidents.

In the Elysian Park area, the transition road from the southbound Golden State Freeway to the southbound Pasadena Freeway was to be blocked until at least this morning by a rockslide. One observer said the slide included a boulder “the size of a Volkswagen.” Caltrans said grading work would have to be done on the hillside before traffic can safely move below it.

Two teen-agers were seen floating down the Santa Clara River in a yellow inflatable boat about 5 p.m. near Lost Canyon and Sand Canyon roads, Sheriff’s Deputy Robert Norlemann said. County firefighters ordered the youths out of the water, and as they got to the bank the boat deflated, Norlemann said.

Smith said search crews also scoured the Santa Clara River in the area of Sand Canyon and Iron Canyon roads where three children were reported entering the river with inner tubes about 5:48 p.m. The youths were later discovered dressed in wet suits, walking along Iron Canyon road, Norlemann said.

Sheriff’s deputies said they had figured out why a man whose truck was swept away in the rain-swollen waters of the San Gabriel River above Azusa had refused offers of assistance.

Raymond Stanley Williams, 27, was left stranded on an embankment after swimming ashore Wednesday afternoon. While he stood there for 3 1/2 hours shivering in the cold rain and ignoring firefighters’ offers of help, deputies checked their records.

Investigators said that when Williams finally relented and accepted their help across the surging river, they arrested him on four warrants--three for driving under the influence and one for vandalism. He also was booked on suspicion of battery on a police officer during the rescue, Sheriff’s Sgt. Sheila Sanchez said.

In Riverside County on Thursday, several cars were trapped and carried away in flash floods when motorists tried to cross normally dry stream beds. The motorists all escaped unharmed.

Mud slid into about a dozen homes in the Pedley area, 5 miles west of Riverside, after a recently graded hillside gave way. Fire officials said several homes, a restaurant, a golf driving range, some business offices and two stables were flooded near Corona. Flooding forced the evacuation of two farm families near Norco.

Muddy water coursed through the streets of residential subdivisions in Hemet, Perris, Moreno Valley and Temecula.

In Ventura County, 11-year-old Darren Hewlett was reported in good condition after being pulled--wet, shivering but otherwise unharmed--from the Arroyo Simi flood control channel.

His rescuers--Mark Harris, 16; James Doll, 15; and Trey Richardson, 15--said they spotted the boy, who had tried to ride down the channel on a boogie board, as he foundered in the fast-moving water.

While Richardson and Harris called police from a nearby motorist’s car phone, Doll climbed over a chain-link fence and lowered his legs toward the water. The boy gripped Doll’s legs and Doll and Richardson helped the boy out of the water, officials said.

The owners of the Ventura Beach RV Resort in the mouth of the Ventura River ordered about 35 campers to leave the park Thursday as showers threatened to repeat the flooding last February that killed a homeless man, damaged a number of recreational vehicles and swept one vehicle out to sea.

The campers were told to stay away until at least Monday.

“It’s not worth the chance to us to maybe have someone hurt,” said Joe Crognale, general manager of the park.

In Orange County, flooding closed one lane of Laguna Canyon Road between the San Diego Freeway and El Toro Road in Laguna Beach. Traffic was open only to northbound traffic in the morning, but was switched for southbound commuters at 3 p.m.

Motorists also had a slow go of it along the Santa Ana Freeway in Tustin, where up to 8 inches of mud and rain covered the northbound lanes of the Santa Ana Freeway, but traffic was still able to move slowly through the flooded area.

About a dozen people were stranded, but safe, in cabins near San Juan Capistrano after San Juan Creek overflowed and wiped out a road, according to the U.S. Forest Service.

Steve Burback, a meteorologist with WeatherData Inc., said the rain should let up this morning, “with the heavy stuff pretty much over by then.”

He said there should be “a few peeks at the sun” this afternoon, but by Saturday, another storm system is expected to begin moving down from Northern California, with rain spreading into Southern California by Saturday afternoon.

Burback said the rain should continue, heavy at times, through Sunday, with up to 2 inches falling in the Los Angeles Basin and substantial snow in the surrounding mountains above 4,000 feet.

“There will be another break on Monday, but not for very long,” he said. “Another system from the eastern Pacific should be in by Tuesday night, with more rain from that one.”

In addition to the 2.21 inches of rain that fell in downtown Los Angeles, other 24-hour totals as of 4 p.m. Thursday included 4.9 inches at Big Bear Lake, 3.44 at Mt. Wilson, 2.57 at Los Angeles International Airport, 2.3 in San Juan Capistrano, 2.23 in Monrovia, 2.02 in Anaheim, 2.0 in Pasadena, 1.7 in Woodland Hills, 1.23 in Torrance and 1.01 in Redondo Beach.

Southland Rain Watch

Rainfall figures for the 24-hour period ending at 4 p.m. Thursday. Season totals and norms are based on precipitation from July 1 to date. L.A. BASIN

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Avalon/Catalina 1.23 2.28 7.55 4.09 Culver City 0.00 1.42 7.57 4.68 Long Beach 2.04 3.10 9.11 6.00 L.A. Civic Center 2.21 3.59 9.43 5.48 L.A. Int’l Airport 2.57 3.96 9.77 4.28 Montebello 1.05 2.55 8.92 4.41 Santa Monica 1.02 2.00 6.12 4.36 Torrance 1.23 2.52 7.75 4.55 UCLA 2.09 3.20 10.37 5.67

VALLEYS/CANYONS

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Beaumont 2.49 4.24 12.92 5.41 Monrovia 2.23 3.85 14.86 NA Northridge 0.00 0.00 3.70 NA Pasadena 2.00 3.77 11.84 6.90 Riverside 2.17 2.99 7.60 3.70 San Bernardino 1.91 3.30 7.70 6.00 San Gabriel 2.13 3.96 13.77 5.91 Santa Clarita 2.55 3.73 9.22 6.10 Woodland Hills 1.70 2.33 9.37 5.72

ORANGE COUNTY

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Anaheim 2.02 3.12 9.91 NA Irvine 0.00 0.00 1.69 NA Laguna Beach 1.10 1.10 2.28 4.56 Lake Forest 1.34 3.01 8.98 NA Newport Beach 1.20 2.36 7.45 4.17 San Juan Cap. 2.30 3.95 9.31 NA Santa Ana 1.74 3.45 8.56 4.30

SAN DIEGO COUNTY

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Chula Vista 1.50 2.30 3.76 3.48 Coronado 1.75 2.51 5.77 NA Del Mar 1.10 2.00 5.97 NA Miramar 0.00 0.51 3.30 NA Oceanside 0.75 1.78 4.69 3.68 San Diego 1.34 2.07 5.11 4.12 Vista 0.00 1.50 5.20 5.16 Alpine 3.60 5.35 13.05 5.66 El Cajon 1.85 3.35 6.03 4.75 Escondido 3.10 4.45 10.02 6.04 Fallbrook 3.40 6.22 12.16 3.10 Poway 2.07 3.01 7.15 4.87 Ramona 2.62 4.63 7.35 5.86

SOUTHLAND MOUNTAINS

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Big Bear Lake 4.90 6.76 16.64 9.85 Cuyamaca Park 0.00 1.68 8.81 12.92 Mt. Laguna 4.86 7.21 20.67 NA Mt. Wilson 3.44 5.45 17.11 12.23 Palomar Mtn. 5.36 9.44 29.77 9.92

DESERTS

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Bishop 0.03 0.03 1.05 2.33 Death Valley 0.00 0.00 0.28 0.92 Lancaster 0.00 0.00 0.70 3.13 Borrego Springs 1.75 2.75 5.23 3.09 El Centro 0.98 1.37 2.54 1.55 Palm Springs 1.33 2.47 4.40 2.87 Thermal 0.09 0.32 1.12 1.73

SANTA BARBARA/VENTURA

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Ojai 0.00 0.23 4.63 6.81 Oxnard 0.68 0.68 3.90 4.95 Point Mugu 1.68 2.21 8.27 NA Santa Barbara 1.06 1.76 7.56 5.80 Santa Paula 1.21 1.21 2.27 5.94 Ventura 1.56 1.93 8.02 4.68

SAN JOAQUIN VALLEY

REGION PRECIPITATION IN INCHES 24-Hour Storm Season Season Total Total* Total Norm Bakersfield 0.47 0.58 4.59 1.95

NA indicates figures not available. In other cases, some totals may be incomplete because of missing station reports.

* Amount of rainfall since the last zero-precipitation day.

SOURCE: National Weather Service and WeatherData Inc.

Contributing to this story were Times staff writers Phil Sneiderman in Simi Valley, Hugo Martin in Los Angeles and Otto Strong in Orange County, and correspondent Kay Saillant in Ventura.