A Coast Guard helicopter flies above the setting sun while patrolling the waters near the Golden Gate Bridge, viewed from Treasure Island Wednesday, Sept. 2, 2020, in San Francisco. Triple-digit temperatures are likely over a vast stretch of the state, and even coastal areas could see higher temperatures, forecasters said. (Jose Carlos Fajardo/Bay Area News Group via AP)
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LOS ANGELES (AP) — Excessive heat warnings began going into effect in California on Friday as forecasters predicted that high pressure building over the western U.S. will send temperatures soaring to dangerous levels during the long Labor Day weekend.

Initial warnings issued for Southern California's valleys, mountains and deserts were expected to expand out to the coast and into Northern California by Saturday.

A “brutally hot" four days are in store, the National Weather Service wrote.

Downtown Los Angeles was forecast to reach 107 degrees (41.6 Celsius) on Saturday and 108 on Sunday (42.2 Celsius). Napa in the wine country could reach 113 degrees (45 Celsius), and Death Valley could broil at about 125 degrees (51.6 Celsius).

The forecasts brought calls to conserve electricity and raised concerns that people flocking to beaches or mountains to escape the heat could spread the coronavirus.

The rush was already on in the popular San Bernardino National Forest east of Los Angeles, where high elevations and lakes offer respite.

“I got a note that most of the campgrounds in the San Bernardino mountain range are already full and I expect them to be completely full within the hour,” forest spokesman Zach Behrens said at mid-morning Friday.

A landscape crew building a walkway in the suburban San Gabriel Valley east of Los Angeles got an early start to avoid some of the worst of the day.

“It cures quicker in the heat so we won’t be able to do it as nicely and it’s a detail job so you want to have it look good,” said Sergio Medina as he and fellow crew members poured concrete.

Fan sales were brisk at Bill’s Ace Hardware store in Concord, east of San Francisco, where temperatures were forecast to reach 106 degrees (41 Celsius) on Sunday.

“We do have people coming in and we’re ready because we brought in a lot of extra fans during the last heat wave,” in mid-August, said store manager Tom Mayer.

For those without air conditioning, cities and counties opened cooling centers in various community buildings and promised compliance with COVID-19 safety measures.

Volunteers with the CHAM Deliverance Ministry in San Jose planned to go out over the weekend to deliver bottled water and sports drinks to homeless people in Silicon Valley.

“When it’s 105 degrees and you’re living in a creek bed in a tent, it’s a lot of health issues out there, it’s a formula for disaster,” said pastor and founder Scott Wagers.

The California Independent System Operator, which runs the power grid, issued a “Flex Alert" for 3 p.m. to 9 p.m. Saturday through Monday, asking people to conserve power by not using appliances and keeping air conditioners at 78 degrees (25.5 Celsius) or above.

Cal ISO also ordered power generators to postpone routine maintenance and restore any out-of-service transmission lines.

Gov. Gavin Newsom declared a state of emergency Thursday night, temporarily suspending certain pollution regulations and permit requirements for power plants so that they can produce more electricity. Ships in port may run auxiliary generators instead of tapping into shore electricity.

The power concern follows a mid-August heat wave that strained the grid to the point where Cal ISO ordered utilities to implement brief rolling blackouts for the first time since 2001. Officials said customers’ conservation significantly helped.

No blackouts were forecast for the Labor Day weekend but officials said the system could be strained by unforeseen problems, such as a fire that disrupts a power line.

Authorities, meanwhile, hoped to prevent a surge in COVID-19 infections that could occur if people engage in traditional Labor Day weekend activities.

COVID-19 infections spiked in many counties after the Memorial Day weekend and again after the Fourth of July weekend as people held gatherings or packed recreational areas.

Los Angeles County did not plan to close beaches. But health authorities warned that could happen if they become too crowded. Masks are required when out of the water.

“My inkling is we will have a lot of people because you can’t really travel, and the next best thing to a Hawaiian beach vacation is an LA beach staycation,” said lifeguard spokesman Pono Barnes.

Other jurisdictions planned to allow people to use beaches for activities such as walking and running but banned sunbathing, towels, coolers and umbrellas. Others banned all beach use other than walking to and from the water.

San Diego's beaches were fully open but people were asked to be mindful of others, said city spokesman Jose Ysea.

“Social distancing is very important, even at the beach," he said.

The heat wave also posed a challenge to thousands of firefighters who have been making progress on numerous wildfires, including massive complexes of multiple fires ignited by lightning last month in the San Francisco Bay Area and wine country.

The high pressure system could produce hot, gusty winds that along with the heat will produce “elevated or near-critical fire weather,” the weather service said.

The Los Angeles Fire Department deployed additional engine crews to areas potentially at risk to enable faster reaction.

The San Bernardino National Forest also upped its firefighting stance.

Behrens, the forest spokesman, said that with few things to do during the pandemic, people have been flocking to the mountains all summer. Many have never camped before, putting a strain on rangers to keep things under control.

Illegal campfires and barbecues outside of designated sites were a particular concern. Behrens said rangers planned to be out in force all weekend on “marshmallow patrols."


Rogers reported from San Gabriel Valley. AP writers Julie Watson in San Diego, Olga Rodriguez, Janie Har and Daisy Nguyen in the San Francisco Bay Area and Michael R. Blood in Los Angeles contributed to this report.