Extreme heatwave hits Southern California. How bad will it be?

A sweltering heat wave is hitting Southern California this week, with the highest temperatures of the summer expected in a region already suffering from oppressive weather.

After a generally mild August in California, a high pressure system is expected to bring temperatures between 5 and 10 degrees above normal on the coast and as much as 20 degrees warmer inland, meteorologists say. The muggiest temperatures are expected between Wednesday and Friday, said Mike Wofford, a meteorologist with the National Weather Service in Oxnard.

“We're talking about four days of continuous heat,” Wofford said. “We've had three or four days of hot weather before, but this is hotter and longer than most other heat waves we've had.”

Temperatures in the San Fernando Valley could range from 43 to 46 degrees Celsius, while downtown Los Angeles is expected to see temperatures between 35 and 37 degrees Celsius. Temperatures in Burbank, Woodland Hills, Pasadena, Santa Clarita and Palm Springs could reach triple digits.

The heat wave in early September follows what climate scientist Daniel Swain says could be the hottest summer on record for much of California. It may not have been as hot as usual on the coast this summer, but it was different in much of the state.

“Most of California's immediate coast has been spared record heat this season (including some of the most densely populated parts of the Southern California Ocean megalopolis). This means that while much of California's land area did indeed experience a record-hot summer, most of California's population probably did not (a pattern that has repeated itself in recent years),” Swain wrote in a post on his Weather West blog.

The weather service issued a heat advisory for most of Los Angeles County from 11 a.m. Wednesday to 8 p.m. Friday, warning the public of peak temperatures of 35 to 43 degrees. Nighttime temperatures between 21 and 25 degrees Celsius are not expected to provide much relief from the heat.

Temperatures are expected to be between 35 and 43 degrees in Long Beach, between 40 and 43 degrees in Antelope Valley and between 38 and 41 degrees in Pasadena and Burbank, Wofford said. In Santa Clarita it could be 41 degrees and in Palm Springs 48 degrees by Thursday.

“This summer will be hotter than ever before, or almost,” he said.

Mayor Karen Bass announced this week that hundreds of cooling centers will be open across Los Angeles by Friday, including “climate stations” on Skid Row where people can find shade, seating and cold drinks. Residents can find a list of cooling centers and “climate stations” online.

In 2020, there was a heat wave at this time of year that brought temperatures as high as 120 degrees in Woodland Hills, traditionally the hottest place in LA, 111 degrees in downtown LA and 114 degrees in Burbank, Wofford said. This heat wave is expected to exceed those levels, but not break them, Wofford said.

Death Valley, the national park known for its sweltering temperatures, recorded its hottest month on record in July. This week's high pressure system is expected to push temperatures in the park up to 48 degrees through Thursday and Friday, just below the July average of 49.9 degrees.

However, temperatures in other parts of California are expected to reach record highs.

Temperatures could reach as high as 45 degrees in the Inland Empire through Thursday and Friday. Temperatures in inland Orange County are expected to reach above 30 degrees, and parts of inland San Diego County could see temperatures as high as 39 degrees, said Philip Gonsalves, a meteorologist with the National Weather Service in San Diego.

And what's the good news about this heat event? It won't be accompanied by Santa Ana winds, reducing the risk of fast-spreading wildfires fueled by gusts even as the Southland simmers.

“There will be a narrow strip of land near the beach where temperatures will be below 90 degrees,” Gonsalves said. “That's because there will still be a marine layer there and we'll still have a sea breeze in the afternoon, whereas with a Santa Ana event there would be no sea breeze.”

Temperatures are expected to drop three to six degrees by Saturday, but will remain above normal for the rest of the weekend, at around 40 degrees in the valleys and between 90 and 95 degrees in downtown LA. Another 2 to 4 degrees of cooling is expected by Sunday and Monday, according to the National Weather Service.

Authorities are reminding Southern California residents to stay hydrated and not leave pets or children in cars as temperatures could get dangerously hot. Vulnerable populations such as pregnant women, the homeless, children, the elderly and people with chronic illnesses are most at risk of heat-related illnesses.

Wofford also warned against doing physical activities such as hiking during the day and rather do them very early or very late in the evening.

“This wouldn't be the best week to do something like that,” he added.