The sweltering heat in the Bay Area on Monday shattered multiple decades-old records, caused a meltdown of the BART system and left thousands of people without electricity.

It got so hot, BART trains experienced major delays systemwide during the evening commute when the heat caused trackway equipment problems.

San Francisco reached a new record high for June 10, with a temperature of 97, shattering the previous record of 88 set in 1985. The normal high temperature in the city on Monday’s date is 66 degrees, officials said..

Across the bay in Oakland, forecasters recorded a high of 98 degrees, breaking the previous record of 92 set in 1994.

Santa Rosa and Gilroy broke records, too. Santa Rosa reached 101 degrees, shattering its record from 1921, when temperatures on June 10 hit 100. Gilroy reached 104 degrees, topping a 2014 record of 102. Kentfield, with 101, tied a 1985 record for the day, and Redwood City also tied a record of 101 degrees set in 1994.

Temperatures in the region climbed a few degrees higher than they did this past weekend, making Monday the hottest day of the year so far, forecasters said.

“It hasn’t been this hot since the big heat wave of 2017,” said Steve Anderson, a National Weather Service meteorologist.

Even coastal locations typically kept cool by the Pacific Ocean breeze were no strangers to heat. In Half Moon Bay, the highest temperature ever recorded for June 10 — 75 degrees in 1941 — was toast as thermometers measured 89 degrees on Monday afternoon, said Anna Schneider, a National Weather Service meteorologist.

“We haven’t seen that surge of clouds, it’ll probably hold off for another day,” Schneider said.

More than 26,000 residents and businesses throughout the Bay Area lost their power as the heat intensified.

According to numbers released by Pacific Gas & Electric company, 14,642 customers in the East Bay suffered outages, while South Bay cutomers reported 5,067. Blackouts hit 4,281 people in San Francisco, 1,824 on the Peninsula and 634 in the North Bay.

Among the areas hit was Fisherman’s Wharf in San Francisco.

The heat also warped tracks on BART Monday afternoon, and crews worked to cool down equipment as delays reverberated throughout the system, according to the transit agency.

Cooler weather may finally abound on Tuesday, with temperatures up to 10 degrees cooler in the forecast.

Weather officials are likely to issue another heat advisory for parts of the inner East Bay, where triple-digit heat is expected for at least one more day.

A shallow marine layer will likely return by Wednesday to bring widespread cooling and return thermometers to normal levels.

“Drink plenty of fluids, stay in an air-conditioned room if possible, or stay in the shade and out of the sun during peak heating hours,” said Scott Rowe, a National Weather Service meteorologist. “Check on your relatives and neighbors.”

The Bay Area Air Quality Management District issued a spare-the-air alert for Tuesday, with air quality in the region measuring as unhealthy for sensitive groups in the eastern part of the region.

Smoke from the Sand Fire in Yolo County, along with other small brush fires burning in Marin and Contra Costa counties could continue to impact air quality. Forecasters said winds could push a thin stream of smoke from the Sand Fire over the North Bay as the blaze continues to burn.

Chronicle Staff Writer Rachel Swan contributed to this report.

Ashley McBride and Gwendolyn Wu are San Francisco Chronicle staff writers. Email: ashley.mcbride@sfchronicle.com gwendolynawu@gmail.com Twitter: @ashleynmcb @gwendolynawu