After a slight cool-down on Labor Day, the weather is expected to heat up for the rest of the week, pushing temperatures in some inland areas past 100 degrees.
There will also be a chance of more humidity, said David Sweet, a meteorologist with the National Weather Service.
"We know it's going to be hot. We're just not sure about humidity," he said.
Highs on Tuesday are forecast to be in the mid-70s to 80s at the beaches and upper-80s to mid-90s inland. Conditions will be hotter in the valleys, with highs for much of the week expected to be in the mid-90s to mid-100s.
The recent hot, humid weather has been caused by a southerly flow transporting air from more tropical locations, including Mexico, to Southern California, Sweet said.