The Monterey Peninsula braces for possible flooding.

Monterey County, the scenic coastal area about 100 miles south of San Francisco that includes Big Sur and the famed golf courses of Pebble Beach, is bracing for flooding that could cut off access to and from the Monterey Peninsula, essentially turning it into an island. The towns of Carmel, Monterey and Pacific Grove are also at risk of being isolated from the rest of the county, local officials said, should floodwaters on critical roadways rise too high.

Officials on Friday prepared for the possibility by positioning ambulances, high-water vehicles and other emergency equipment in the areas that could be isolated by rising waters, Maia Carroll, the communications coordinator for Monterey County, said. Those areas include Highways 1 and 68, which are vulnerable to flooding from the Salinas River.

“We’re beginning to see that high-water effect,” Ms. Carroll said, explaining that private farm levees and berms along the Salinas River had been breached by the flooding. More than 17,000 residents were under evacuation warnings or orders as of Friday, and the county was operating six emergency shelters for evacuees, including on the county’s fairgrounds, she said.

Rachel Sarchet, the general manager at Lighthouse 4 Cinema, a movie theater in Pacific Grove, a city at the northern tip of the peninsula, expressed concern about the weekend storms but was more worried about possible power outages than flooding.

“When storms like this happen, we get a lot of blackouts,” she said. “And then of course, we can’t sell any tickets or anything like that.”

If the lights do go out, Ms. Sarchet plans to follow protocol: Tell moviegoers in the auditorium to wait at least five minutes to see if the power returns. If it does not, then Ms. Sarchet will escort them safely out of the building and close down for the day.

While flooding has already stranded some commuters near the theater, it is less of a worry for Ms. Sarchet’s co-workers, who live in town, no more than 10 minutes away. She herself walks to work.

But a few miles down the road in Monterey, Holly Eichrodt, who works at Fieldwork Brewing Company, said her managers cut down on staffing in anticipation of Saturday’s storm, telling most employees who had shifts scheduled not to come in.

“I’ve got a co-worker that lives in Salinas,” Ms. Eichrodt said. “She’s on call, but I don’t think that she should come in because what if she couldn’t get home?”

Victoria Kim contributed reporting.