LOS ANGELES (AP) — With spring still a week away, it was already starting to feel like summer Thursday in Southern California as temperatures topped 90 degrees — an unusual March heat wave that forecasters warned could put people at higher risk for illness.

It’s expected to be about 20 degrees warmer than normal for mid-March through Friday, the National Weather Service said. Officials opened cooling centers and urged residents to drink a lot of water and avoid outdoor activities during the daytime.

The winter heat wave comes from a combination of high pressure and a lack of cooling winds blowing in from the Pacific Ocean, said Bryan Lewis, a meteorologist at the weather service’s office for Los Angeles.

“The nation’s air conditioner, as we like to call it, is essentially shut off right now,” Lewis said Thursday. “We’ll likely tie or break several temperature records all across LA County.”

The hottest day around Los Angeles will be Thursday, with the mercury hitting 91 degrees shortly after noon in some neighborhoods. It could reach 95 degrees in the San Fernando Valley, Lewis said. Temperatures are typically around 70.

Workers doing outdoor construction will have plenty of drinking water and electrolyte packets available to stay hydrated.