Intense storm to wallop Bay Area on Wednesday

A car heads through a flooded intersection near Lakeshore Avenue on Tuesday Dec. 2, 2014 in Oakland, Calif. A car heads through a flooded intersection near Lakeshore Avenue on Tuesday Dec. 2, 2014 in Oakland, Calif. Photo: Mike Kepka / The Chronicle Photo: Mike Kepka / The Chronicle Image 1 of / 28 Caption Close Intense storm to wallop Bay Area on Wednesday 1 / 28 Back to Gallery

An intense storm — expected to cause widespread damage and flooding — will slam the Bay Area with heavy rain and high winds midway through the week, forecasters said.

The blast, the likes of which only hit Northern California once every few years, will swing in sometime around Wednesday evening and continue into Friday. Winds in some areas will gust up to 50 mph and close to 4 inches of rain may drench urban areas, said Steve Anderson, a forecaster with the National Weather Service.

“We haven’t seen this kind of rain in almost two years now,” he said. “It won’t take much to saturate the ground, so we may get flooding and mudslides. The rain is a little out of the ordinary, but the wind will be the most damaging part of the storm.”

A storm last week brought much needed rain to drought-ravaged California, but also caused havoc across the region. Urban floodwaters cascaded down San Francisco’s sloping neighborhoods and pooled around city streets. Several sinkholes opened up around the city while commuters and travelers were brought to a sliding halt on wet Bay Area highways.

Wednesday’s system will be stronger.

“The last storm dumped a lot of rainfall and the ground is still saturated,” Anderson said. “This will be much worse. Expect the same thing but on a more widespread scale — more intense.”

Drought-stressed trees with weak root systems will be even more vulnerable to the pummeling winds as the ground continues to saturate, creating “a recipe for massive amounts of trees going down,” Anderson said.

Cities around the Bay Area may experience power outages as debris cuts power lines and blocks roadways. Thousands of people were left without power after last week’s storm, which had much weaker winds, forecasters said.

“We know there is a large storm coming in this week,” said Jana Morris, a spokeswoman for Pacific Gas and Electric Co. “We have crews on standby and we will work around the clock to get customers power back on.”

PG&E officials urged residents to treat all downed power lines as live wires and to stay away.

The storm is part of a powerful, deep low-pressure system building in the Gulf of Alaska. The front will start moving south early in the week and hit sometime around the Wednesday evening commute, according to the weather service.

Heavy rain and high winds will be steady overnight into the Thursday morning drive-time, continuing through Friday. The heaviest hit areas will be the North Bay and the Santa Cruz Mountains, which may see more than 5 inches of rain, Anderson said.

The weather system also will whip up the surf. Waves around 15 and 18 feet will wallop the Bay Area’s coastline making any activity on the water extremely dangerous.

The region will only see a small amount of precipitation Monday, and Tuesday will be dry for the most part.

“If anyone needs to be preparing for the storm, Tuesday will be the only day,” Anderson said.

The system will continue into the Sierra where it will dump 1 to 2 feet of snow around 6,000 feet, well below mountain pass levels.

Evan Sernoffsky is a San Francisco Chronicle staff writer. E-mail: esernoffsky@sfchronicle.com Twitter: @EvanSernoffsky