"Avoid outdoor activities during the hottest part of the day, typically between 10 a.m. and 4 p.m.," Rabrich said. "People also must stay hydrated by drinkng fluids like water or Gatorade."
Avoid alcohol, he advised, since it can act as a diuretic and lead to dehydration.
There is, however, the danger of overhydration -- also known as "water intoxication" -- so Pellegrino advised drinking about a half a cup of water every 20 minutes if participating in outdoor activities.
Proper wardrobe choices will also help keep cool -- wear loose-fitting clothing and a hat if out in the sun.
And since the situation is even more dangerous for the elderly and infirm, more able-bodied people should check in on neighbors, loved ones and friends to be sure they are keeping cool and watch for signs of heat exhaustion or heat stroke. Those who are socially isolated may also need someone to check on them.
Although extreme heat and humidity can bring misery and health hazards, people don't have to fall victim to the weather -- as Pellegrino said, "Heat emergencies are totally preventable."