Anyone working or exercising outside risk dehydration and heat-related illnesses.
And while the mercury will skyrocket Monday, temperatures are expected to be even higher Tuesday and Wednesday, with meteorologists predicting the heat to peak Tuesday for areas west of the mountains and on Wednesday farther inland.
The high today for Fallbrook is expected to hit 89 degrees, but by Tuesday, highs are predicted to hit triple digits.
An excessive heat warning goes into effect Sunday morning as temperatures continue to rise across the Southland, creating an "elevated fire danger" that will extend into next week, according to forecasters. Highs will hover around the 100 degree mark for the remainder of the week.
Desert areas bore the brunt of the high temperatures, with Borrego Springs reaching 113 degrees.
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Alpine also set a new record low of 76 degrees on Thursday, while both Vista and Ramona both tied their previous records for the day.
On Tuesday, San Diego is forecasted to hit 91 degrees, which would break the previous August 29 record of 88.
Dangerously hot weather is expected in the majority of the Bay Area.
The smoke and heat should start to disappear by Tuesday of next week, she said, as westerly winds help clear out smoke and keep temperatures in the upper 80s.
Lancaster reached 105 on Saturday, the weather service tweeted.
What's the difference? Here are definitions for each term, straight from the National Weather Service. Take precautions to avoid heat illness.