Fall Heat Wave Ups Fire Concerns In The Bay Area: Forecast

SAN FRANCISCO — A late-season heat wave will bring triple-digit temperatures and elevated fire risks to much of the Bay Area for much of the week as the latest forecasts trend hotter, drier, and windier. Forecasters said the triple threat could create red flag conditions in some areas over the next few days.

A heat advisory that took effect Monday morning across the Bay Area was upgraded to an excessive heat warning for many inland areas of the North Bay, East Bay and Santa Clara County. The advisories and warnings will remain in place until at least Wednesday evening, but forecasters said some would likely be extended.

Tuesday could end up being the hottest day of the week for many, when afternoon highs are forecast to hit triple digits in Concord, Fremont, Hayward, Hollister, Livermore, Napa, Redwood City, San Jose, San Mateo, San Rafael, Santa Rosa and Sunnyvale. Forecasters expect San Francisco will inch closer to 90 degrees as coastal areas heat up, too.

"During the peak of this heat wave, inland areas will reach the mid-100s while coastal locations will be in the 80s to mid-90s," the weather service said Monday. "Offshore winds are bringing very dry conditions to higher elevations, particularly in the North Bay. As such, fire weather conditions will be elevated through the week with critically dry fuels and gusty winds at night."

The weather service said the factors behind the heat wave are unusual for October and could make for a heat wave like the one recorded exactly 44 years ago.

"That heat wave brought 3 days of 90+ degrees to downtown SF, with a peak of 97 recorded on the 1st," NWS Bay Area said. "We could very well see similar impacts this week."

Forecasters expect persistent offshore winds will continue to create elevated fire risks through at least Wednesday afternoon, especially at higher elevations, with poor overnight recoveries of both temperature and humidity. The return of onshore winds could begin to bring coastal communities relief on Thursday, but inland areas could stay 15 to 20 degrees hotter than normal for a few days longer.

"The latest guidance shows a gradual cooldown through the weekend and into the early part of next week," the weather service said. "However, the guidance trend over the last few days has been to extend the duration of this heat wave."