Updated 12:59 pm, Sunday, June 18, 2017
Photo: Nicole Boliaux, The Chronicle
It is a rare San Francisco day where you can probably leave your sweater behind.
The sun was already beating down early Sunday with temperatures hovering around 80 degrees at 10 a.m. — about 20 degrees more than the average for a morning in June. Temperatures were expected to keep rising in the Bay Area throughout the day, with some inland areas hitting the mid to upper 90s.
“This whole heat event will be the most substantial heat wave we’ve had this season,” said Charles Bell, a meteorologist for the National Weather Service in Monterey.
San Francisco hit 88 degrees Sunday, beating the record set in 1993 for June 18, but Bell said the existing record for this day “is not really that high.” Saturday’s historic high is 95, while Monday’s is set at 92.
“If the wind kicks in, then that will be it for the day — but if not, some spots could get into the lower 90s,” he said.
Other records in danger of falling were in Oakland, which hit a 93 degrees in 1962, and San Jose, with a record of 99 set in 1945.
Breaking any records Monday is “very unlikely,” Bell said. “Sunday’s heat is probably the peak for the entire event,” although the heat wave is expected to last well into the week. By Friday, Bell said the high pressure system lingering overhead will move toward the east, allowing cooler weather to work its way back in.
“It’s not an unprecedented heat wave,” Bell said. “We typically will have several periods every year where we’ll get very warm to hot weather … usually we’ll get this two to three times a year.”
But just because it’s happened before, doesn’t mean the weather-weary Bay Area residents are prepared.
“Be careful about leaving children and pets in cars, and please be aware that the vehicle will heat up to a dangerous level very fast,” he said. “Take plenty of breaks, and drink water.”
A Spare the Air alert was in effect for the Bay Area Sunday as the combination of hot temperatures and traffic exhaust threatened to create unhealthy air quality. The California Department of Forestry and Fire Protection also issued a red flag warning for the Central Sacramento Valley, which means the area’s hot and dry conditions made it vulnerable to wildfires. The red flag warning was expected to last until 9 p.m. Sunday.
Because of the rarity of such heat waves, many homes near the coast do not have air conditioning. Bell said residents who need refuge from the heat should seek out their local cooling centers. Many Bay Area municipalities have with air conditioning that are open to the public when temperatures exceed certain levels.
Or, he said, people could just go to the beach.
“It is pretty remarkable how the temperature drops off just a little closer to the ocean,” he said.
Trisha Thadani is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: