Southern California faced scorching heatwaves this summer that made locals wonder what happened to their famed Mediterranean climate.

Now, the fall is bringing heatwaves too.

Friday kicked off a new round of long-duration heatwave advisories from the National Weather Service (NWS), which expects unseasonably high temperatures to linger for at least a week. Temperatures are expected to hover near 100F in downtown Los Angeles, and spike well into the triple digits farther inland, raising the risk of both heat-related illness and wildfires.

“We’re expecting temperatures will run some 15-20 degrees above normal – that’s pretty significant,” said Richard Bann, a meteorologist with the NWS’s Weather Prediction Center. “Stay cool. Stay hydrated. Limit exposure to the sun.”

October heatwaves are not uncommon in southern California. They’re caused by ridges of high air pressure that park themselves above the region. This year, they’re also influenced by an ongoing marine heatwave that, in turn, is driving a strong El Niño – a year of above-average surface-water temperature in the Pacific Ocean.

But experts say the severity and duration of this year’s fall heatwave is extreme, and likely to become more common in the future as the climate crisis nudges global temperatures higher.

“The extremely hot temperature Friday is rare,” said V Kelly Turner, a professor of geography and urban planning at UCLA. “Nearly 7F hotter than the hottest October 2 ever and about 30 degrees higher than historical averages around 75F.”

If there’s a silver lining for southern California, it’s that current forecasts do not call for strong winds that would threaten to fuel and spread wildfires – though the increased heat and low soil moisture still makes them more likely.

It’s difficult for scientists to point to a specific event and describe it as an effect of climate change, said David Neelin, an atmospheric physicist who researches climate change at UCLA.

But research is showing that with every half-degree of global warming, heatwaves become both more likely and longer lasting.

“Overall, it’s hard to escape that a warmer climate adds to the strength of heatwaves,” Neelin said. “It adds to the probability of heatwaves and the likelihood of getting longer-duration heatwaves.”

This week’s heatwave will coincide with major outdoor events in the region, including the first game of the National League division series between the LA Dodgers and the Atlanta Braves on Saturday, noted Edith de Guzman, a researcher who studies climate change and heat adaptation at UCLA. She urged political governments to invest in heat adaptation now to make the region more livable in the future. Providing more shade is the most “most effective way to keep people safe”, she wrote in a text message.

“Climate change is making longer-duration heatwaves possible, while simultaneously increasing their frequency and intensity,” De Guzman wrote. “So we should prepare for more of this in the future.”