It's so hot in SoCal. Here's how to stay safe.

A heatwave that kicked off after Labor Day in the western U.S. will keep bringing dangerous temperatures to millions of people this weekend, and some of the worst heat is settling on Southern California.

On Friday, Downtown Los Angeles reached a heat index of 112 degrees, the third time the area has reached that level since 1877, the local NWS office said on social media . An excessive heat warning is still in effect in Los Angeles County.

In San Diego and Orange counties, coastal towns will reach around 90 degrees while some inland suburbs should hit near 110 degrees. Palm Springs will be a sweltering 112 degrees Saturday.

Meanwhile in Oregon and Washington, hot temperatures have also prompted red flag warnings for wildfire risk in the Cascade Mountains, the NWS Portland office said.

Heat can cause serious illness or death, the Centers for Disease Control and Prevention says . People are at greater risk if they are elderly, younger, work outside, have underlying health conditions or don’t have air conditioning or are homeless.

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The Los Angeles City Fire Department recommended people plan ahead and avoid going out during the hottest times of the day.

In a Friday afternoon social media post , Erik Scott, an LAFD spokesperson, said people should hydrate even when they’re not thirsty; stay cool with shade outside, and air conditioning and fans inside; take cold showers or baths; and dress down with cotton or linen. Additionally, people should check on other people, especially those who are greater risk of illness from heat. Lastly, Scott said, people should not leave children or pets in parked cars, since temperatures can double quickly inside.

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This summer has been the world's hottest on record , Copernicus , Europe's climate change service, said on Friday.

This article originally appeared on USA TODAY: It's so hot in SoCal. Here's how to stay safe.