Bay Area Cities Swelter as Temperatures Near Triple Digits

After an unusually cool summer in the Bay Area, national weather officials have issued moderate heat risk advisories to cities both inland and coastal, with some areas experiencing the longest heat wave so far this year.

Temperatures in the Bay Area ticked up Tuesday, jumping 10 degrees by Wednesday. Cities like Santa Rosa, San Rafael and Napa are forecasted to approach triple digits on Thursday — marking the first time they hit 100 degrees this year.

The North, South and East Bay, as well as Monterey and San Benito County, are all under a moderate heat risk advisory through Saturday.

The Peninsula — including San Francisco, Half Moon Bay and San Mateo counties — is under the same advisory through Thursday, with temperatures expected to fall significantly by Friday. The National Weather Service will hold a minor heat risk warning for the Peninsula, as Friday will still see temperatures well into the 80s.

NWS meteorologist Dylan Flynn told KQED the entire summer went by without a single heat wave advisory, which is “not normal at all.”

The last recorded heat advisory was May 31, which Flynn said is starkly different from what the Bay Area experienced around this time last year.

“Last year, by this time, we had 23 days under a heat advisory for some portion of the Bay Area,” Flynn said. “So this summer has been cool and we’re kind of snapping out of that today.”

Flynn said the warm-up — a term weather officials typically use unless there is an excessive, extreme heat advisory in place — may impact residents more intensely than in years past “due to a lack of acclimatization,” thanks to the cooler summer.

Flynn said that a big difference between this heat wave and past recorded ones is that humidity is a significant factor, whereas, regularly, heat waves in the Bay Area have been dry.

“When it’s humid, the sweat kind of stays on you, and it doesn’t cool you off as well,” Flynn said. “What that does is just increases your body temperature, and that’s what we’re concerned about.”

The NWS has been issuing safety messaging to emergency management partners in affected areas, Flynn said.

Santa Clara County opened cooling centers designated for more vulnerable populations like the unhoused and elderly, with free bus rides to transport them.

Despite the heat, inland cities like Concord and Napa will continue monitoring the heatwave and will not open cooling centers at this time. City officials encouraged residents to keep pets cool, limit sun exposure and stay hydrated.

Flynn said that although weather officials haven’t issued specific advisories related to schools, as the academic year is back in session for most districts, there is general guidance for students to be vigilant in the heat.

He said taking breaks in the shade and staying as hydrated as possible are some best practices for preventing heat stress.

Lauren Schwartz, from the San Rafael City Manager’s office, told KQED that city staff have also been dealing with a large structure fire affecting residents, but said the office has an advisory online in place for residents to use for safety.

Flynn estimated that temperatures will start to cool off by Sunday, although it will be a gradual return to normal.

“There’s not like a big cold front coming that’s going to bring noticeable relief right away,” he said. “By the time we get to the middle of next week, we should be closer to normal temperatures.”