Heat: A Major Killer


  1. Introduction
  2. Heat Index Information
  3. Heat Hazards
  4. How Fast Can the Sun Heat A Car?
  5. Heat Safety
  6. Effects of Excessive Heat


Heat is the number one weather-related killer in the United States. NOAA National Weather Service statistical data shows that heat causes more fatalitiesSunset on a hot summer day per year than floods, lightning, tornadoes, and hurricanes combined. Based on the 10-year average from 1994 to 2003, excessive heat claimed 237 lives each year. By contrast, floods killed 84; tornadoes, 58; lightning, 63; and hurricanes, 18.

In the disastrous heat wave of 1980, more than 1,250 people died. In the heat wave of 1995 more than 700 deaths in the Chicago, Illinois area were attributed to this event, and in August 2003, a record heat wave in Europe claimed an estimated 50,000 lives.

North American summers are hot; most summers see heat waves in one section or another of the United States. East of the Rockies, they tend to combine both high temperature and high humidity although some of the worst have been catastrophically dry. Additional detail on how heat impacts the human body is provided under "The Hazards of Excessive Heat" heading.


NOAA's Watch, Warning, and Advisory Products for Extreme Heat


Excessive Heat Outlook: when the potential exists for an excessive heat event in the next 3 to 7 days. An outlook is used to indicate that a heat event may develop. It is intended to provide information to Heat Index forecast map for the contiguous United States those who need considerable lead time to prepare for the event, such as public utilities, emergency management and public health officials.

Excessive Heat Watch: when conditions are favorable for an excessive heat event in the next 12 to 48 hours. A watch is used when the risk of a heat wave has increased, but its occurrence and timing is still uncertain. It is intended to provide enough lead time so those who need to set their plans in motion can do so, such as established individual city excessive heat event mitigation plans.

Excessive Heat Warning/Advisory: when an excessive heat event is expected in the next 36 hours. These products are issued when an excessive heat event is occurring, is imminent, or has a very high probability of occurrence. The warning is used for conditions posing a threat to life or property. An advisory is for less serious conditions that cause significant discomfort or inconvenience and, if caution is not taken, could lead to a threat to life and/or property.


How Forecasters Decide Whether to Issue Excessive Heat Products

NOAA's heat alert procedures are based mainly on Heat Index Values. The "Heat Index", sometimes referred to as the "apparent temperature" and given in degrees Fahrenheit, is a measure of how hot it really feels when relative humidity is added to the actual air temperature.

To find the heat index, look at the Heat Index Chart. As an example, if the air
temperature is 96°F (found on the top of the table) and the relative
humidity is 65% (found on the left of the table), the heat index-or how
hot it really feels-is 121°F. This is at the intersection of the 96°
column and the 65% row. The National Weather Service will initiate alert procedures when the Heat Index is expected to exceed 105°- 110°F (depending on local climate) for at least two consecutive days.

Heat Index temperature chartIMPORTANT: Since heat index values were devised for shady, light wind conditions, EXPOSURE TO FULL SUNSHINE CAN INCREASE HEAT INDEX VALUES BY UP TO 15°F. Also, STRONG WINDS, PARTICULARLY WITH VERY HOT, DRY AIR, CAN BE EXTREMELY HAZARDOUS.

Note on the Heat Index Chart shaded zone above 105°F. This corresponds to a level that may cause increasingly severe heat disorders with continued exposure and/or physical activity.



The Hazards of Excessive Heat

Too Much Heat

Heat disorders generally have to do with a reduction or collapse of the body's ability to shed heat by circulatory changes and sweating, or a chemical (salt) imbalance caused by too much sweating. When heat gain exceeds the level the body can remove, or when the body cannot compensate for fluids and salt lost through perspiration, the temperature of the body's inner core begins to rise and heat-related illness may develop.

Ranging in severity, heat disorders share one common feature: the individual has overexposed or over exercised for his age and physical condition in the existing thermal environment.

Sunburn, with its ultraviolet radiation burns, can significantly retard the skin's ability to shed excess heat. Studies indicate that, other things being equal, the severity of heat disorders tend to increase with age--heat cramps in a 17-year-old may be heat exhaustion in someone 40, and heat stroke in a person over 60.

Acclimatization has to do with adjusting sweat-salt concentrations, among other things. The idea is to lose enough water to regulate body temperature, with the least possible chemical disturbance.




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Children, Adults, and Pets Enclosed in Parked Vehicles Are at Great Risk

Each year children die from hyperthermia as a result of being left enclosed in parked vehicles. Hyperthermia is an acute condition that occurs when the body absorbs more heat than it can dissipate. This can occur even on a mild day.  Studies have shown that the temperature inside a parked vehicle can rise rapidly to a dangerous level for children, adults, and pets.  Leaving the windows slightly open does not significantly decrease the heating rate. The effects can be more severe on children because their bodies warm at a faster rate than adults.

This graph shows            hyperthermia deaths from 1998 through 2004

Hyperthermia deaths aren't confined to the summer months only. They also happen during the spring and fall. Below are some examples.

  • Hawaii, March 07, 2007: A 3 year old girl from Honolulu died from hyperthermia. The child's father told police that he left her in a child seat in the back seat of the car for an hour and a half  late Saturday morning while he visited friends in a Makiki apartment building.  The outside temperature was only 81 degrees. 
  • North Augusta, SC; April 2006: A mother left her 15 month old son locked in a car. He was left in the car for 9 hours while his mom went to work. She is currently serving a 20 year prison sentence.
  • Denver Aug 2008: Two kids that died in an overheated car may have been on their own for more than 3 hours as their mother slept after working a night shift.  The kids died in a closed but unlocked car, investigators believe the temperature where the children were found may have reached 123 degrees.

Adults are also susceptible to hyperthermia. On July 12, 2001 a man died of heatstroke after falling asleep in his car with the windows rolled up in the parking lot of a supermarket in Hinds County, Mississippi.



The atmosphere and the windows of a car are relatively “transparent” to the sun’s shortwave radiation (yellow in figure below) and are warmed little.  However this shortwave energy does heat objects that it strikes.  For example, a dark dashboard or seat can easily reach temperatures in the range of 180 to over 200 degrees F.

These objects (e.g., dashboard, steering wheel, childseat) heat the adjacent air by conduction and convection and also give off longwave radiation (red) which is very efficient at warming the air trapped inside a vehicle.

Objects Heated by the Sun Warm Vehicle's Air

( Hi-Res ~ 2.5 mb.WMV file)
Individual Frames:
(Animation Courtesy of General Motors and Golden Gate Weather Services)

Heat Safety

Child Safety Tips

  • Check to make sure seating surfaces and equipment (child safety seat and safety belt buckles) aren't too hot when securing your child in a safety restraint system in a car that has been parked in the heat.

Heat Wave Safety Tips

  • Slow down - Strenuous activities should be reduced, eliminated, or rescheduled to the Thermometer on a hot summer daycoolest time of the day. Individuals at risk should stay in the coolest available place, not necessarily indoors.
  • Dress for summer- Lightweight light-colored clothing reflects heat and sunlight, and helps your body maintain normal temperatures.
  • Put less fuel on your inner fires - Foods (like proteins) that increase metabolic heat production also increase water loss.
  • Spend more time in air-conditioned places - Air conditioning in homes and other buildings markedly reduces danger from the heat. If you cannot afford an air conditioner, spending some time each day (during hot weather) in an air conditioned environment affords some protection.
  • Don't get too much sun - Sunburn makes the job of heat dissipation that much more difficult
  • Do not take salt tablets unless specified by a physician


Know These Heat Disorder Symptoms

SUNBURN: Redness and pain. In severe cases swelling of skin, blisters, fever, headaches. First Aid: Ointments for mild cases if blisters appear and do not break. If Example of a severe sunburnbreaking occurs, apply dry sterile dressing. Serious, extensive cases should be seen by physician.




*For more information contact your local American Red Cross Chapter. Ask to enroll in a first aid course.


Community Guidance: Preparing for and Responding to Excessive Heat Events

The "Excessive Heat Events Guidebook" was developed by the Environmental Protection Agency (EPA) in 2006, in collaboration with NOAA's National Weather Service (NWS), the Centers for Disease Control and Prevention (CDC), and the U.S. Department of Homeland Security (DHS). This guidebook provides best practices that have been employed to save lives during heat waves in different urban areas, and provides a menu of options that communities can use in developing their own mitigation plans.

Produced as a cooperative effort of NOAA's National Weather Service, the Federal Emergency Management Agency, and the American Red Cross.

