Midnight is the drenching hour as storms head to L.A.

Southland residents braced for a wet weekend as rain made its way down from Northern California and was set to arrive in Los Angeles about midnight, setting the stage for a series of major rainstorms that could unleash as much as 5 inches of rain in Los Angeles and 10 inches in the mountains through Sunday.

“There’s no way out. This is a big low-pressure system with a lot of moisture.... It definitely has us in its sight,” said climatologist Bill Patzert.

Forecasters said the first major storms of 2008 could cause the most significant rainfall in Southern California since January 2005. That winter, near-record rains triggered dangerous mudslides.

The storms were shaping up just as forecasters expected. The first rains, which should be light to moderate, are expected to hit Los Angeles around midnight, Patzert said.

The National Weather Service predicted that the most powerful system, expected Friday, would bring “strong and possibly damaging winds.” Forecasters predicted gusts of up to 70 mph in the mountains and the Antelope Valley, and warned that downed trees and power lines were likely.

In Orange County and the Inland Empire, forecasters expect up to 3 inches of rain, with up to 8 inches in the mountains, through Sunday.

“It’s three storms wedged one after another, with the middle one being the largest,” said Patzert, who works at NASA’s Jet Propulsion Laboratory in La Cañada Flintridge.

Friday’s storm is expected to bring light to moderate rainfall in the morning, with the downpour intensifying in the afternoon and overnight.

“If this delivers as advertised, we haven’t seen something like this for three years, so it will be a shocker,” Patzert said.

Forecasters warned that burned areas could be hit by mudslides beginning Friday night. They also said the heavy rain could cause urban and small streams to flood, and they warned of potential “life-threatening flash flooding.”

“Once we get into the rain on Saturday, that’s when the problems could start because the ground is already wet,” said Stan Wasowski, a weather service forecaster in San Diego.

A flash-flood watch was issued for the recent burn areas from Friday morning through Saturday morning.

Another inch of rain could fall Sunday.

The last time Los Angeles saw more than 3 inches of rain in a single month was February 2005, when 11.02 inches of rain hit downtown Los Angeles. In January of that year, 9.32 inches of rain fell on L.A., the same month a mudslide hit the coastal Ventura County enclave of La Conchita, killing 10 people.

The 2004-05 rainy season nearly set a record, with more than 37 inches of rain falling on L.A., more than double the annual average of nearly 15 inches.

But weather experts say they don’t think this rainy season will break any records.

“The forecast is still for a dry winter, and that’s largely based on the presence of La Niña this year,” said Kelly Redmond, interim director of the Western Regional Climate Center at the Desert Research Institute in Reno.

Redmond said this year’s La Niña, a cooling of ocean temperatures along the equator from the International Date Line to Peru, has helped keep the jet stream focused on the Pacific Northwest, which has been pelted by storms in recent weeks.

“We’ve looked at this relationship over the past 75 years, and we haven’t seen above-normal rainfall years with La Niña,” Redmond said. He added that the central Sierra were seeing only 50% to 55% of the average year’s snowpack.

Still, he said, “I’ve been surprised thus far with the vigor of the storms” in Southern California.

By now, people should be well prepared for wet weather, officials said.

“We’ve had enough rehearsals with the last two rainstorms ... that people are pretty aware. We just want to remind them to continue to be vigilant,” said Brad Davis, emergency services coordinator for Malibu.

Kirsten James, water quality director with Santa Monica-based Heal the Bay, advised people to avoid going to the beach during and after the storms, as the rains flush trash and other debris into creeks, bays and coastal waters.

“There will be all this bacteria that has built up and is being washed down,” James said. “We advise [residents] to stay out of the water 72 hours after a storm event.”

Lifeguards at county beaches enjoyed calm waters today, though the storm was expected to bring significant surf along the coast starting Friday, said Capt. Terry Harvey, spokesman for the lifeguard division of the Los Angeles County Fire Department.

U.S. Coast Guard officials said they expected waves of up to 15 feet by Saturday.

“This is definitely not a time for new or inexperienced boaters to be out on the water,” Coast Guard Lt. Andrew Munoz said.

ron.lin@latimes.com

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