A heat wave that already has left behind more fire will hit its peak Monday as temperatures again soar into the triple digits and high 90s in the Bay Area, before relief starts to trickle in on Tuesday, weather forecasters said.

“This is gonna be the hottest day of the week,” National Weather Service meteorologist Roger Gass said Monday morning. “Right now, we’re seeing a southerly surge happening near the Big Sur coast, and it’s working its way up the coastline. So we’ll see a return of the on-shore winds, and that will cool things down gradually as we head through the week.”

The key word, according to forecasters, is “gradually.” Temperatures will come down from the 100s, but they still will hover in the low to mid-90s through much of the work week, while also getting into the 80s along the coast, forecasters said. On Monday, temperatures were expected to get as high as 103 degrees in Livermore and Antioch in the far inland East Bay, 97 degrees in San Jose, and 90 in San Francisco.

A heat advisory remained in effect throughout the region.

“It’s going to be warm and dry through the interior into the middle of the week,” Gass said.

The southerly flow that’s gaining momentum eventually will push the thermometer back down and will “relax and ease” the strong wind gusts that were present through the weekend and into Monday morning, Gass said. Those winds reached up to 50 mph in the highest elevations and were responsible for a red flag warning through 9 p.m. Monday in the North Bay and East Bay Hills and interior valleys.

The North Bay already was under siege after the Glass Fire broke out Sunday near Santa Rosa. Twenty-five wildfires were burning in the state, according to the California Department of Forestry and Fire Protection, including one in Shasta County that has burned 15,000 acres and was zero percent contained Monday morning.

Those fires along with others that have burned for weeks in Plumas and Butte counties could end up dirtying the air again, though Gass said “there are a lot of unknown factors at this point.”

The Bay Area Air Quality Management District extended a Spare the Air alert through Friday, and some air in the North Bay already had become bad enough in the North Bay to unhealthy for people with breathing or other underlying conditions. In San Francisco, the air-quality index reading at 7 a.m. was 102, and in Sebastopol it was 107.

Much of the region had readings between 51-100, considered moderately unhealthy. One exception was in Gilroy, where the AQI of 42 still was good.

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