A heat wave is a prolonged period of excessively hot weather, which may be accompanied by excessive humidity. The term is relative to the usual weather in the area, so temperatures that people from a hotter climate find normal can be a heat wave if they are outside the normal pattern for a cooler area. The term is applied both to "ordinary" weather variations and to extraordinary spells of heat which may only occur once a century.
Some regions of the globe are more susceptible to heat waves than others, such Mediterranean-type climates with a summer dry spell which on certain years becomes much hotter than usual.
To remain safe during heat waves, see " class="external">http://chicago.about.com/library/blank/bl_hot_weather_tips.htm
Major Heat Waves