Temperatures are expected to stay in the 90s for most areas and get hotter throughout the week, with the warmest day likely on Friday. For the Valleys and the Inland Empire, the mercury will hit triple digits later in the week. There's also a chance of thunderstorms for the local mountains and High Desert communities.
The National Weather Service said an extreme heat watch may be issued later this week.
Around 1 p.m., with the temperature near 100 degrees, one Southland high school cross country runner collapsed. Paramedics say she's going to be OK. She was taken to the hospital as a precaution. They say it's a reminder to take it easy during the heat wave.
"In this elevated heat in the San Fernando Valley, Santa Clarita Valley, Antelope Valley, you definitely have to take precaution. You have to hydrate," said Capt. Al Bustillos with the Los Angeles County Fire Department. "Those that don't absolutely require training in the middle of the day, we would recommend that you don't train in the middle of the day. Perhaps get your workout in early."
As early as 9:30 a.m., the San Fernando Valley was already pushing 80 degrees. At Lake Balboa, joggers and walkers were definitely feeling the heat as they tried to finish their morning workout.
The first day of autumn is Sept. 22 - a date many Southlanders say they're looking forward to.
"I'm ready for the fall. It's my favorite time of year, and I'm ready for this heat to be over," said Tarzana resident Desmond Slater.
For Wednesday, a high of 80 was forecasted for Newport Beach, 84 at Los Angeles International Airport, 94 in downtown Los Angeles, 96 in Anaheim, 97 in Long Beach, 99 in the Antelope Valley, 101 in Pasadena and Burbank and 103 in Woodland Hills.
Forecasters say overnight lows will also be warmer than usual, ranging from the mid-to high-60s in the valleys and low-to mid-70s in the Antelope Valley and communities at the foothills of the San Gabriel Mountains.