Southern Californians will get a holiday reprieve from the hot, muggy weather of recent days before the heat returns later in the week, forecasters say.

The weather will cool down and dry out slightly Monday but will heat up again midweek with 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 of the midweek forecast.

High temperatures Monday are expected to be in the 70s at the beaches and in the lower to middle 80s inland. By Wednesday, highs are forecast to be in the mid-70s to 80s at the beaches and upper-80s to mid-90s inland.

The valleys can expect highs in the mid-80s to mid-90s on Labor Day, and in the mid-90s to mid-100s Wednesday through Saturday.

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.

A flash flood watch is in effect from 11 a.m. Sunday through the evening for the Los Angeles County mountains, the Ventura County mountains, the Antelope Valley, and the Santa Barbara mountains. 

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Twitter: @Sam_Schaefer

Samantha.Schaefer@latimes.com