Northern California residents were bracing for a powerful storm expected to be the biggest in five years as a torrent of atmospheric moisture originating near Hawaii barreled toward the West Coast Wednesday.

The National Weather Service issued a high wind and flash flood warning for areas in and around the San Francisco Bay and north up the western Washington coast.

The storm was expected to pelt the region through Thursday. It could overwhelm waterways and roadway drainage systems, possibly leading to flash flooding.

This storm is 'expected to be one of the strongest storms in terms of wind and rain intensity' since storms in October 2009 and January 2008, respectively, said the National Weather Service in Monterey.

'Pineapple express': An atmospheric river of moisture was expected on Wednesday to bring a massive storm capable of dumping the most rain seen since 2005 on some areas of Northern California

Lashing: The storm was expected to start lashing western Washington on down to the San Francisco Bay on Wednesday

Good and bad: Flash flood warnings were issued by the state of California, but heavy snowfall was expected to benefit the state as forecasters said it would fall in areas hit hard by three years of drought

Heavy rainfall is expected, especially in the North Bay.

According to Accuweather.com, Sacramento could see as much as six inches of rainfall in just a couple of days--the most in that period of time since 2005.

Overall, the heaviest rainfall totals are expected from western Washington to Northern California, with numerous 3- to 5-inch rainfall totals expected.

Mark Ghilarducci, the director of the California Governor's Office of Emergency Services, issued a warning that the storm will present a risk of flash flooding and debris slides.

'This year was also a significant fire season for Northern and Southern California and burned areas are especially at risk for debris slides. Even regions that don't experience regular seasonal flooding could see flash flooding during this intense storm system, which could be the largest to date of this year's rainy season,' he said in a statement.

High winds from 20 to 40 mph are expected, with gusts of 40 to 60 mph.

Authorities are warning motorists to avoid driving through standing water; stay clear of outside roadway lanes, especially at night; keep headlights on at all times; and drive slowly to prevent hydroplaning. People should also have emergency contacts available and a stock a small emergency kit that can sustain each person for three days.

Some projections said rainfall in Sacramento could reach levels not seen since a 2005 storm

PINEAPPLE EXPRESS ATMOSPHERIC RIVER: A BLESSING AND A CURSE FROM HAWAII The so-called 'Pineapple Epxress' is an atmospheric river of moisture that often brings major weather events to North America's Pacific Coast. The system is named for its origins in Hawaii, around where it gets its massive moisture content. Via NOAA.gov: Atmospheric Rivers (AR) are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics. While ARs come in many shapes and sizes, those that contain the largest amounts of water vapor, the strongest winds, and stall over watersheds vulnerable to flooding, can create extreme rainfall and floods. These events can disrupt travel, induce mud slides, and cause catastrophic damage to life and property. However, not all ARs cause damage – most are weak, and simply provide beneficial rain or snow that is crucial to water supply. An average of between 30 to 50 percent of the total precipitation for the year on the West Coast comes from ARs. The biggest events among them can transport in the form of water vapor between 7.5 and 15 times the average flow of liquid water at the mouth of the mighty Mississippi. How a typical Pineapple Express 'atmospheric river' event works Advertisement

Farther north, a series of strong weather fronts with high winds and heavy rains could lead to flooding and landslides this week in western Washington state.

The National Weather Service expects as much as 14 inches of rain between Monday and Thursday in the Olympic Mountains west of Seattle. And it expects as much as 13 inches of rain in the North Cascades east of the city.

Saturated soils will bring the risk of mudslides, while winds could topple trees.

Last week, a different Pacific system brought three days of rain to Southern California.

There was some flooding and evacuations near hillsides stripped bare by wildfires, but the Los Angeles area avoided major damage despite some huge rainfall totals. An exceptional 14.5 inches fell between Tuesday and Thursday at Yucaipa Ridge in the San Bernardino Mountains, the National Weather Service said.

Most other parts of the state received 2 to 4 inches of rain.

The storm dropped snow in mountains key to the state's water supply and made signature waterfalls flow at Yosemite National Park, including the 2,425-foot Yosemite Falls that had slowed to a trickle in mid-July.

Meanwhile, Southern California was hit by a different storm system just a week before. That system hung around for days and caused mudslides in areas of Ventura County where wildfires had stripped vegetations