Thousands of Californians evacuated due to “Pineapple Express” flood

Thousands of people have been forced to evacuate as a “Pineapple Express atmospheric river" brought a deluge of rainfall to the north of California.

Residents have also been warned not to drink tap water, as officials fear the flood water may be contaminated with chemicals.

Across the Central Coast's Monterey County, more than 8,500 people were under evacuation orders and warnings Saturday.

The Pajaro River, separates the counties of Santa Cruz and Monterey, burst its banks - officials said the its levee breach is about 100 feet (30.48 metres) wide.

Emergency crews went door to door on Friday afternoon to urge residents to leave before the rains came.

Some of those who stayed had to be pulled from floodwaters early Saturday.

First responders and the California National Guard rescued more than 50 people overnight.

One video showed a member of the Guard helping a driver out of a car trapped by water up to their waists.

“We were hoping to avoid and prevent this situation, but the worst case scenario has arrived with the Pajaro River overtopping and levee breaching at about midnight," wrote Luis Alejo, chair of the Monterey County Board of Supervisors, on Twitter.

Alejo called the flooding “massive,” saying the damage will take months to repair.

Floodwaters in the region’s wells might be contaminated with chemicals, officials said, and residents were told not to drink or cook with tap water for fear of illness.

Officials had been working along the levee in the hopes of shoring it up when it was breached around midnight Friday into Saturday.

Crews began working to fix the levee around daybreak Saturday as residents slept in evacuation centres.

Gov. Gavin Newsom's office on Saturday said it was monitoring the situation in Pajaro.

“Our thoughts are with everyone impacted and the state has mobilized to support the community,” the governor's office wrote on Twitter.

The Pajaro Valley is a coastal agricultural area known for growing strawberries, apples, cauliflower, broccoli and artichokes.

What is an atmospheric river and why has this one been named Pineapple Express?

An atmospheric river is a huge area of moisture in the sky which helps carry saturated air from the tropics to higher latitudes, delivering unrelenting rain or snow.

Typically 250 to 375 miles wide, atmospheric rivers can stretch more than a thousand miles long, the National Oceanic and Atmospheric Administration says.

This particular atmospheric river is known as a “Pineapple Express” because it brought warm subtropical moisture across the Pacific from near Hawaii, which was melting lower parts of the huge snowpack built in California’s mountains.

This week's storm marked the state’s 10th atmospheric river of the winter.

The storms have brought enormous amounts of rain and snow to the state and helped lessen the drought conditions that had dragged on for three years.

Yet another atmospheric river is already in the forecast for early next week as well as another round of heavy, wet snow is expected to hit the Sierras and areas of high elevation mid-week.

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