The blanket of Bay Area heat that the National Weather Service anticipates will rise into triple digits in some areas and the high 90s in many others Friday won’t set any records for length of duration — temperatures are set to be as much as 15 degrees cooler by Sunday — but may be just as dangerous as the longer ones, according to weather and safety officials.

“People around the region should be very mindful of that,” NWS meteorologist Matt Mehle said Friday. “It is a dangerous day, especially for people who are vulnerable to the heat such as the elderly and small children. Since we’re not acclimated to the summer heat yet and it’s such a spike, this is a scenario that could be very impactful for them.”

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The arrival of 2025’s first heat blast has been in the works since earlier this week, and all the conditions that weather forecasters anticipated were in place Friday morning, Mehle said. The expected results is that weather service said temperatures are expected to reach 102 to 103 degrees in far east Contra Costa County; 97 in Morgan Hill in the Santa Clara Valley; 96 in Livermore in far east Alameda County; 97 in Concord; 94 in Walnut Creek and Pleasanton; and 90 in San Jose.

Closer to the water, the temperatures will be warm but not quite as intense. The weather service said San Mateo is likely to reach 78, Richmond 77 and Oakland 76. San Francisco will be excluded altogether; high temperatures there are not expected to get above 67,

Such temperatures with such little time for the body to acclimate to them is not a recipe for an easy adjustment, officials said.

The weather service issued a heat advisory for the Santa Clara Valley and Eastern Hills; the East Bay hills and valleys, the Santa Cruz Mountains, interior Monterey County and the Santa Lucia Range beginning at 11 a.m. It is set to expire at 8 p.m.

“This level of heat affects most individuals sensitive to heat,” the weather service wrote in the advisory. “Especially those without effective cooling and/or adequate hydration.”

In addition, the Bay Area’s first Spare the Air alert for 2025 also was in effect. The Bay Area Air District issued the alert on Thursday in anticipation of what it called unhealthy smog levels.

The heat also will bring with it “elevated fire concerns,” according to the weather service, even though winds are expected to be almost non-existent throughout the hottest spots in the region.

“You’ll have normal afternoon breezes,” Mehle said. “So while that’s a good thing, the fire conditions are still elevated. You look at the hills and a lot of the green is gone. They’re brown now. And it’s those hot, dry, flashy fuels like dried up grass that can really burn.”

The hot day is serving as a preview of sorts for what may be longer and possible hotter runs later in the summer, according to the weather service. The most intense heat will last only 24 hours in most parts of the region, though Mehle said some areas on the far interior in eastern Contra Costa County could hit 100 degrees again on Saturday. In places such as Concord, Walnut Creek, Livermore, San Jose and the Santa Clara Valley, the dial is expected to drop 3-4 notches.

On Sunday, most of the high temperatures in the region won’t escape the mid-70s.

“The high pressure that’s bringing our heat is fading,” Mehle said. “A trough of low pressure from the Pacific Northwest is going to come across the state and it’s going to be a blast of that natural air conditioning.”

According to the weather service, it’s too early to tell when the next significant heat spike may occur and how long the next one may last.

They remain all too concerned about this one, short as it may be.

“Don’t mistake it for being any less dangerous,” Mehle said.