The excessive heat warning is in effect from noon until Wednesday at 8 p.m.
Temperatures are expected to hit triple digits in many areas of the Southland, and outdoor activities are not recommended in such extreme heat.
Aileen Finch was up early to exercise at the Rose Bowl in Pasadena before the sun came up.
"You heat up quickly, and you can get sun stroke, so I would get it done early or late at night," she said.
Beaches, rivers and lakes will likely be busy, as people try to beat the heat. Stores say they has been a jump in those buying fans and portable air conditioners.
Heat wave safety tips
- Drink more fluids. Don't wait until you're thirsty.
- Don't drink alcohol or sugary liquids because they dehydrate you.
- Wear light, loose-fitting clothing.
- If possible, stay in cool, air-conditioned place.
- Never leave people or pets in a parked vehicle.
- If you must be in the heat, limit outdoor activity and cut down on exercise.