SAN FRANCISCO (CBS SF) — A threat of Diablo winds, blasts of hot, extremely dry gusts from the northeast of up to 35 mph, has triggered a Red Flag warning for the already parched North Bay hills beginning Wednesday evening.

The National Weather Service issued the warning for prime wildfire conditions from 11 p.m. Wednesday through Thursday morning.

“A shift towards a drier air mass and offshore flow will lead to locally critical fire weather conditions across the interior North Bay Mountains tonight through Thursday morning,” the weather service warned. “Locally gusty north to northeast winds overnight will coincide with poo humidity recoveries.”

Sustained winds in the range 10-25 mph with gusts up to 35 mph were predicted.

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At the highest risk, forecasters said, is “the interior North Bay mountains including the Vaca & Mayacamas ranges across Napa County and into interior Sonoma County.”

There has been an active wildfire season already this year, particularly in the eastern Sierra where more than 2.5 million acres have burned and hundreds of homes have been destroyed including much of the communities of Greenville, Canyondam and Grizzly Flats.

The latest of the blazes, the Dixie Fire, was at 94% containment on Wednesday morning and had burned 963,309 acres.

“October is just a few days away and is historically a very active month for fire weather in the last several years, with the Wine Country, Kincade, and other notable fires,” the weather service said.

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More than 2,000 firefighters were on the lines of the Windy Fire burning on the Tule River Indian Reservation and in Sequoia National Forest, including Giant Sequoia National Monument.

The fire had scorched more than 133 square miles after growing by nearly 11 square miles in 24 hours, according to a Sequoia National Forest statement. Just 2% of the fire was contained.

Numerous small communities were under evacuation orders or warnings to be prepared to leave. Some 2,000 residences and 100 commercial properties were threatened. Two commercial structures have been destroyed.

To the north in Sequoia National Park, two fires that were ignited by lightning and then merged covered more than 73 square miles after experiencing large growth during the weekend. The KNP Complex was 8% contained, according to a statement from Sequoia and Kings Canyon national parks, which have both been forced to close.