LOS ANGELES -- California authorities are urging people living in an area devastated by mudslides to evacuate ahead of a strong Pacific storm that forecasters say is likely to bring an extended period of rain and the threat of flooding and debris flows. Santa Barbara County issued a mandatory evacuation order Monday affecting about 30,000 people, including the community of Montecito, where 21 people were killed by a massive mudslide in January.

CBS Los Angeles reports the evacuation order will take effect at noon on Tuesday for the Thomas, Whittier and Sherpa burn areas. Montecito, which has faced mud slides and flooding in recent months, could see as much as 4 inches of rain.

Residents won't be forcibly removed if they choose to stay but Sheriff Bill Brown urged them to prioritize their safety despite potential evacuation fatigue.

Get Breaking News Delivered to Your Inbox

"We understand the process of evacuating is tiring and frustrating, and we know that it is an extraordinary hardship on everyone being asked to leave their homes or to close their businesses once again," he said at a news conference. "We know that it is disruptive, costly and inconvenient. Please know that we would not be making this decision without it being our belief that it is necessary to protect your safety."

Brown said county officials reached the decision because "there is enough rain on the way to trigger a potential debris flow that could threaten life and property."

"We have no choice really but to do this," he said. "It is simply not worth risking lives to avoid evacuations."

National Weather Service meteorologist Mark Jackson said the storm is likely to be the strongest so far this winter.

"There's a tremendous amount of moisture coming up out of the Pacific," he said, adding that the key to the storm will be its lengthy duration.

Preliminary rainfall estimates for the so-called atmospheric river range from 2-5 inches across coastal and valley areas and 4-6 inches on south-and southwest-facing foothills and mountains, forecasters said, adding that local amounts up to 10 inches can't be ruled out.

Where exactly the peak rainfall will occur was still uncertain, but meteorologists said it seemed likely it would be Santa Barbara County.

A stretch of the county's south coast was hit hard by a storm on Jan. 9, unleashing massive debris flows from scorched mountains above the community of Montecito. Hundreds of homes were damaged or destroyed, 21 people were killed and two still remain missing.

The storm was also expected to spread rain up the coast through the San Francisco Bay region and eastward to the Sierra Nevada, where a flash flood watch will go into effect Wednesday from about Yosemite southward.