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Heat Waves

Heat Index Chart / NWS Alert Procedures


A heat wave is an extended interval of abnormally hot and usually humid weather, usually lasting from a few days to over a week.


Heat waves form when an air mass becomes stationary over a region. Hot humid air masses form over the Gulf of Mexico and the Caribbean Sea while hot dry air masses form over the desert Southwest and northern Mexico. In the Eastern United States a heat wave occurs when a high pressure system originating in the Gulf of Mexico becomes stationary just off the Atlantic Seaboard (typically known as a Bermuda High.) The SW winds on the back side of the High continue to pump hot, humid Gulf air North-eastward resulting in a spell of hot and humid weather for much of the Eastern States.


Heat Waves are dangerous because heat kills by taxing the human body beyond its abilities. In a normal year, about 175 Americans succumb to the demands of summer heat. Among the large continental family of natural hazards, only the cold of winter - not lightning, hurricanes, tornadoes, floods, or earthquakes - takes a greater toll. In the 40-year period from 1936 through 1975, nearly 20,000 people were killed in the United States by the effects of heat and solar radiation. In the disastrous heat wave of 1980, more than 1,250 people died. The July 1995 heat wave caused more than 1,000 heat-related deaths across the Midwest and East Coast. And these are the direct casualties. No one can know how many more deaths are advanced by heat wave weather - how many diseased or aging hearts surrender that under better conditions would have continued functioning.


A heat advisory is issued when the heat, or combination of heat and humidity, is expected to become an inconvenience for much of the population, and a problem for some.


An excessive heat warning is issued when the heat, or combination of heat and humidity, is expected to be dangerous for a large portion of the population.


The heat index is the number in degrees Fahrenheit that tells how hot it really feels when relative humidity is added to the actual air temperature. Exposure to full sunshine can increase the heat index by 15 degrees Fahrenheit.

130 degrees or higher: heatstroke/sunstroke highly likely with continued
105 - 130 degrees: sunstroke, heat cramps or heat exhaustion likely with prolonged exposure.
90 - 105 degrees: sunstroke, heat cramps and heat exhaustion possible with prolonged exposure and/or physical activity.
80 - 90 degrees: fatigue possible with prolonged exposure and/or physical activity.

The National Weather Service (NWS) will initiate alert procedures when the heat index is expected to exceed 105 -110 degrees Fahrenheit for at least two consecutive days.

Are You at Risk?

Extreme heat is more than an issue of discomfort. It forces the body into overdrive as it tries to stay cool through perspiration and evaporation. People in urban areas are at greater risk because the stagnant atmospheric conditions trap pollutants in the air, which, when breathed can trigger respiratory problems for many people.

The effects of extreme heat can undermine you physical well being so slowly and subtly that the dangers aren't apparent until it's too late. Heat can effect anyone, however, it is more likely to affect young children, elderly people, and people with health problems. (Example - A medical condition that causes poor blood circulation and those who take medicine to get rid of water from the body {diuretics} or for certain skin condition, may be more susceptible. Consult a physician if you have any questions about how your medication may affect your ability to tolerate heat).

In regions of low humidity, the most common human response to extreme heat is dehydration. Exposed to direct sunlight and temperatures in excess of 90 , a human can lose as much as half a gallon of water every ten minutes, and this dehydration can seriously interfere with one's internal thermostat.

Heat-Related Illnesses

  • Severe Sunburn - so much more that a dermatological issue, sunburn reduces the skin's ability to release excess heat, making the body more susceptible to heat-related illnesses.
  • Heat Cramps - muscle pains and spasms caused by heavy exertion, which triggers loss of water through heavy perspiration. These usually involve the muscles of the abdomen or legs.
  • Heat Exhaustion - a mild form of shock marked by heavy sweating, weakness, cold, clammy skin, a weak pulse, fainting and vomiting. This usually occurs when people have been exercising heavily or working in a warm humid place. The blood flow to the skin increases -- in an attempt to cool the body -- causing the blood flow to the vital organs to decrease. If not treated the victim's condition will worsen. Body temperature will keep rising and the victim may suffer heat stroke. Simple overexposure to extreme heat can precipitate this condition in very young children and the elderly.
  • Heat Stroke (also called Sunstroke) - a truly life-threatening condition in which the body's internal thermostat has ceased to work. The victim's temperature control system, which produces sweating to cool the body, stops working. The body temperature can rise so high that brain damage and death may occur in less than ten minutes unless medical help is immediate.

Signs and Symptoms to Look For:

  • Heat Cramps - Painful spasms usually in muscles or legs and abdomen. Heavy sweating.
  • Heat Exhaustion - Cool, moist, pale or flushed skin, heavy sweating, headache, nausea or vomiting; dizziness; and exhaustion. Body temperature will be near normal.
  • Heat Stroke - Hot, red skin; changes in consciousness; rapid, weak pulse; and rapid, shallow breathing. Body temperature can be very high, sometimes as high as 105 . If the person was sweating from heavy work or exercise, skin may be wet; otherwise, it will feel dry. Treatment for These Conditions:
  • Heat Cramps - Get the person to a cooler place and have him or her rest in a position of comfort. Give a half of glass of cool water every 15 minutes. Remember: Do not give liquids with alcohol or caffeine in them, as they can make conditions worse.
  • Heat Exhaustion - Remove the person from the heat and into a cooler place. Remove or loosen tight clothing and apply cool and wet cloths, such as towels or sheets. If the person is conscious, give cool water to drink. Make sure the person drinks slowly.
  • Heat Stroke - Life Threatening situation. Help is needed fast - Call 911. Move person to a cooler place. Quickly cool the body. Immerse victim in a cool bath, or wrap wet sheets around the body and fan it. If vomiting or change in level of consciousness is presented, do not give any thing by mouth.

Heat Wave Tips:

  1. If a heat wave is predicted or happening - slow down. Avoid strenuous activity. If you have to do strenuous activity the recommended hours are between 4 am and 7 am.
  2. Stay indoors as much as possible. If air conditioning is not available, stay on the lowest floor, out of the sunshine. Remember electric fans do not cool air, but they do help sweat evaporate which cools your body.
  3. Wear lightweight, light colored clothing. Light colors will reflect away some of the sun's energy.
  4. Drink plenty of water regularly and often, even if you do not feel thirsty. Your body needs water to keep cool.
  5. Water is the safest liquid to drink during heat emergencies. Avoid drinks with alcohol or caffeine in them. They can make you feel good briefly, but make the heart's effects on your body worse. This is especially true about beer, which actually dehydrates the body.
  6. Eat small meals and eat more often. Avoid foods that are high in protein, which increase metabolic heat.

Suggestions for Places to Go During a Heat Wave

  • Local Mall
  • Library
  • Senior Citizen's Center
  • A movie theater
  • A restaurant
  • A home of a friend or relative

REMEMBER: Check on elderly friends and neighbors.





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