NOAA produces a HEAT index chart that helps determine the risk for Heat Stress.
CDC - Healthy safe summer recommendations. - Protect from Sun, Swim safety, Safe boating, Move, Drink water, and leave the fireworks to the professionals.
According to CBS NEWS, revised heat stroke guidelines from the National Athletic Trainer's Association (NATA) advises immediate cooling before transferring to a hospital.
Basic principles: keep hydrated with water (no caffeine or alcohol) , rest more often, use shade or air conditioned space. It is important to adapt to higher temperatures by gradually increasing the amount of time in the heat. Drink water even when not thirsty.
Heat stroke and heat exhaustion are serious conditions that can occur. With heat stroke, the person will often be belligerant, irrational and may be hallucinating.
Treatment of heat stroke