Wildfires have charred more than 108,000 acres on the North Coast this season, but firefighters are bracing for more trouble this month with a tinder-dry landscape and no soaking rain coming soon.

At a time when it would typically be closing stations and laying off seasonal firefighters, Cal Fire remains on alert with its major natural nemesis — a dry offshore wind — expected this week.

Winds up to 70 mph propelled Oakland's firestorm, the most destructive blaze in state history, over the East Bay hills in October, 1991. The four-day fire, which killed 25 people, also destroyed more than 3,300 homes and did about $1.5 billion worth of damage.

Temperatures are expected to be moderate this weekend and next week, with daytime highs in the 60s and 70s in Santa Rosa, and some light rain is possible but Cal Fire is bracing for offshore winds along the North Coast starting Wednesday and continuing through Oct. 15.

"That's what we're concerned about," Cal Fire spokesman Daniel Berlant said. Dry wind blowing from California's sunbaked interior is the "biggest challenge" in containing a wildfire, he said.

Offshore winds are the opposite of the region's normal summertime flow, which brings in damp, cooler air from over the ocean.

Cal Fire already has responded to more than 5,300 wildfires this year, 1,300 more than last year and nearly 20 percent more than average, Berlant said.

On the North Coast, 16 major fires in Cal Fire territory and on federal lands have scorched more than 108,000 acres. Sonoma County has largely been spared, with only one significant blaze, a 40-acre fire along Highway 101 south of San Antonio Road on Aug. 8.

But three fires — two in Colusa County and one in Mendocino County northeast of Covelo — covered nearly 90,000 acres, more than 80 percent of the region's total.

And the 272,000-acre Rush fire in Lassen County in August became California's second most extensive wildfire in history.

The worst wildland blaze in Sonoma County history, the Hanly fire, roared from Calistoga to Chanate Road, covering more than 50,000 acres, on a windy day in September, 1964.

Nature set the stage for a worrisome fire season with a mild, dry winter that "never allowed us to catch up," followed by a typically arid summer, Berlant said.

Nearly all of Northern California is designated bright red — indicating "above normal fire potential" — in Cal Fire's monthly outlook for October.

No significant rain is expected through at least the third week of the month, the report says. One or two inches or rain won't help much if it's followed by dry, breezy weather than dries out the grass and brush, Berlant said.

It takes at least three inches of rain in a short period to soak the fuel that sustains wildfires, he said.

Nothing like that is expected until late October, "if then," he said.