Areas of the Antelope Valley and Inland Empire are expected to stay above 100 all week, with the hottest areas potentially reaching 111 degrees in the desert on Wednesday and even up to 120 in Palm Springs.
Downtown Los Angeles, however, will remain cooler - in the 80s and low 90s - while the beaches will remain pleasant with temperatures in the 70s all week.
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Doctors say it can take some time to get acclimated to truly hot temperatures, so people who stay outdoors too long could be taken by surprise.
For that reason, the first few days of a heat wave can be the most dangerous.
"It takes the body a while, even a few weeks to really acclimatize to exerting yourself in a higher heat environment," said Dr. Marc Judd with Adventist Health.
For those who are outside during the daytime, experts recommend frequent hydration, and it should start prior to the heat exposure.
For example, someone who weighs 150 pounds should consume about 14 ounces of water every two hours in the heat.
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Of course, frequent application of sunscreen is also recommended. Stay away from caffeine, energy drinks and other stimulants that increase the heart rate.
Other tips include monitoring the mental state of any elderly friends or family members. If they seem confused, they could be suffering from heat exhaustion. Kids, too, are vulnerable to dizziness and exhaustion in the heat.
All around the Southland, people were looking for ways to cool off. Many families flocked to pools, such as the Rose Bowl Aquatics Center, which can see up to 4,000 visitors a day in the summer.
Even the pool water can get uncomfortably warm on a hot day, so the facility has installed a high-powered spout to help keep it cool.
"They found that it was so hot at that time that if they could take the water from the bottom of the pool, throw it up in the air and gain a little bit of moisture and put it back on the pool surface, it cooled the top 6-8 inches of the pool and made it feel cooler," said Kurt Knop, executive director of the Rose Bowl Aquatics Center.