CONCORD >> A mid-autumn wind storm that was gearing up Thursday to blitz the Bay Area with significant force brought with it the threat of public safety power shut-offs for about 8,000 PG&E customers.

PG&E Bay Area Regional Vice President Jake Zigelman said that the shutdowns could begin by Thursday afternoon. “We will monitor in real time and have a ‘go or no-go’ on whether to go ahead with (the shutdown) at that time.”

The wind speeds were expected to gain strength as Thursday progressed, further drying out the already brittle vegetation. The conditions have created severe fire conditions that brought a red-flag warning for the entire region set to take effect at 11 p.m. Thursday and expire at 5 p.m. Saturday.

A wind advisory also was set to go into effect late Thursday night for the interior areas of the East Bay, the eastern Santa Clara hills and the North Bay mountains. Isolated wind gusts could be as high as 65 mph, but they were expected to blow steadily between 25-35 mph and gust regularly at 40 mph, according to the weather service.

As a result, humidity levels were expected to plummet. The relative humidity in Oakland was 90% at 5 a.m. Thursday, according to the weather service. By 5 a.m. Saturday, it was expected to be about 30%. In some of the hottest areas, it may sneak below 25%.

Winds with less force and an atmosphere with better humidity gave rise to a big wildfire in Contra Costa County just two years ago.

All of those factors affected PG&E’s decision, Zigelman said. He added that PG&E’s shutdown, if it happened, would include rural parts of Alameda, Contra Costa, Santa Clara, Santa Cruz, Napa, Solano and Sonoma counties.

Zigelman said the utility decides where to pull the plug through a process called public scoping.

“When we see the fire risk danger, we try to see where the most dangerous spots are and how those spots are interacting with our circuits,” he said. “What customers are being served by those circuits?”

Zigelman said information on when and where in each county the shutdowns would occur is available on the utility’s website at pge.com. The utility in a statement said it would notify all affected customers no less than four hours before a public safety power shut-off.

Officials also warned that the winds could knock out power to other areas where outages are not planned.

The extreme fire danger in the Bay Area is everywhere, officials said. On Wednesday, the weather service added the Santa Cruz County area to a red- flag warning that already had included the Peninsula, the Bay Shoreline and downtown San Francisco, places where such warnings are rare.

Other counties outside the Bay Area got better news from the utility. PG&E said rainfall in the Northern and Central Sierra Nevada on Wednesday allowed them to remove Alpine, Amador, Calaveras, El Dorado, Nevada, Placer, San Luis Obispo, Sierra and Tuolumne counties from the list of planned shutdowns.

The dangerous weather is a result of a low-pressure system that’s tracking over land and creating offshore winds blowing toward the ocean. Those conditions are not unusual for this time of year, nor is the fact that fire conditions will remain high even though temperatures will be relatively low. The hottest spots in the region are not expected to get much past the mid-80s.

“It’s tricky because you look at our history books. We’ve had fires in December. We’ve had them in January. We’ve had them when the temperatures are in the 40s, 50s and 60s,” NWS meteorologist Matt Mehle said. “So you don’t need to have the hot temperatures to have the fire concerns.”