HEAT – THE NUMBER ONE NON-SEVERE WEATHER RELATED
KILLER IN THE UNITED STATES

August 2, 2006 — The summer of 2006 is far from over and already more than 150 people in the United States have died as a direct result of heat. More above normal temperatures are expected for much of the nation throughout the month of August, as has been the case in the continental U.S. for all of 2006, according to the NOAA National Climatic Data Center in Asheville, N.C.

Of all the natural hazards in the United States, heat is the number one non-severe weather related killer. Unlike the roar of an approaching tornado, heat waves kill with silence. In an average year, about 175 Americans succumb to the effects of summer heat, according to the NOAA Office of Climate, Water, and Weather Services and the NOAA National Climatic Data Center. 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. Through improved heat-wave forecasting, plus greater public awareness and education, NOAA is working to help reduce the number of heat-related deaths.

Heat Waves Can Strike Almost Anywhere in the United States
North American summers are hot; most summers see heat waves in one section or another of the United States. East of the Rockies, heat waves tend to combine both high temperature and high humidity, although some of the worst heat waves have been catastrophically dry (as was experienced in California this summer).

Cities in the northeastern and midwestern United States typically have the strongest weather mortality relationships because weather variability, rather than heat intensity, is the single most important factor in defining human sensitivity to heat. People living in highly variable summer climates are not well adapted to extreme heat, mainly because it occurs irregularly. As a result, temperate cities like Philadelphia, Boston, Chicago and New York exhibit extreme increases in the number of deaths reported when an intense heat wave occurs compared to many more tropical cities. This is one reason that early season heat waves are associated with higher mortality — because people within the city population acclimate to the heat as the hot season continues.

The NOAA National Weather Service Heat Index Program
The NOAA National Weather Service has stepped up its efforts to more effectively alert the general public and appropriate authorities to the hazards of heat waves — those prolonged excessive heat/humidity episodes.

Based on the latest research findings, the NOAA National Weather Service has devised the “Heat Index,” (sometimes referred to as the “apparent temperature”). The Heat Index, given in degrees Fahrenheit, is an accurate 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 to the right. As an example, if the air temperature is 95 degrees Fahrenheit (found on the left side of the table) and the Relative Humidity is 55 percent (found at the top of the table), the Heat Index — or how hot it really feels — is 110 degrees Fahrenheit. This is at the intersection of the 95 degrees Fahrenheit row and the 55 percent column. (Click NOAA image for larger view of the NOAA Heat Index Chart. Click here for high resolution version. Please credit “NOAA.”)

Summary of the NOAA National Weather Service Heat Alert Procedures
The NOAA National Weather Service will initiate alert procedures when the Heat Index is expected to exceed 105 degrees Fahrenheit - 110 degrees Fahrenheit (depending on local climate) for at least two consecutive days. The procedures are:

• Include Heat Index values in zone and city forecasts.
• Issue Special Weather Statements and/or Public Information Statements presenting a detailed discussion of:
  • Extent of the hazard, including Heat Index values
  • Who is most at risk
  • Safety rules for reducing the risk.
• Assist state/local health officials in preparing Civil Emergency Messages in severe heat waves. Meteorological information from Special Weather Statements will be included as well, as more detailed medical information, advice and names and telephone numbers of health officials.
• Release to the media and over the NOAA Weather Radio All Hazards all of the above information.

The Heat Index used in issuing NOAA’s heat alerts should not be confused with another related, yet different variable — NOAA’s Mean Heat Index. The Mean Heat Index is a measure of how hot the temperatures actually feel to a person over the entire course of the day. It differs from the traditional Heat Index in that it is an average of the Heat Index from the hottest and coldest times of each day.

"Heat waves often turn fatal when the nighttime temperature doesn't drop very much from a high daytime temperature," said Jim Hoke, director of the NOAA Hydrometeorological Prediction Center in Camp Springs, Md., where the Mean Heat Index originates. "The Mean Heat Index captures this potentially serious condition by including data from what should be a cooler portion of the day, and factoring that in to give a ‘big picture' of the day's temperatures, not just the day's high."

According to NOAA scientists, a Mean Heat Index above 85 degrees Fahrenheit is considered dangerous. The Mean Heat Index is issued to the public via both graphical and text formats, giving local health and emergency officials advanced warning when a prolonged period of dangerous heat approaches. "Having more time to warn the public increases the chances of saving lives," added Hoke.

How Heat Affects the Body Human
Human bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands and — as the last extremity is reached — by panting when blood is heated above 98.6 degrees Fahrenheit. The heart begins to pump more blood, blood vessels dilate to accommodate the increased flow, and the bundles of tiny capillaries threading through the upper layers of skin are put into operation. The body’s blood is circulated closer to the skin’s surface, and excess heat drains off into the cooler atmosphere. At the same time, water diffuses through the skin as perspiration. The skin handles about 90 percent of the body’s heat dissipating function.

Sweating, by itself, does nothing to cool the body, unless the water is removed by evaporation, and high relative humidity retards evaporation. The evaporation process itself works this way: the heat energy required to evaporate the sweat is extracted from the body, thereby cooling it. Under conditions of high temperature (above 90 degrees Fahrenheit) and high relative humidity, the body is doing everything it can to maintain 98.6 degrees Fahrenheit inside. The heart is pumping a torrent of blood through dilated circulatory vessels; the sweat glands are pouring liquid (including essential dissolved chemicals, like sodium and chloride) onto the surface of the skin.

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 (See call out boxes below entitled "KNOW THESE HEAT DISORDER SYMPTOMS" and "HEAT INDEX/HEAT DISORDERS").

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

Cities Pose Special Hazards
The stagnant atmospheric conditions of the heat wave trap pollutants in urban areas and add the stresses of severe pollution to the already dangerously high temperatures, creating an even more serious risk for health problems.

The high inner-city death rates also may be attributed to the lack of/poor ventilation and/or air conditioning — particularly in dwellings constructed of materials such as brick that can trap hot, humid air at dangerous levels. While air conditioning may be a luxury in normal times, it can be a lifesaver during heat wave conditions.

The NOAA Heat Health Watch/Warning System
The NOAA Heat Health Watch/Warning System measures oppressive air masses affecting health and is part of a national focus on the special hazards excessive heat has on urban centers. As a result, this highly customized system enhances NOAA’s ability to issue accurate and timely heat-related advisories, watches and warnings and inform the public to take action to avoid the health risks associated with periods of unusually high heat.

Seventeen metropolitan areas in the United States are now a part of the NOAA National Weather Service’s Heat Health Watch/Warning System. Cities Currently with the Heat Health Watch/Warning System include: Portland, Ore.; Dallas/Fort Worth, Texas; Phoenix, Ariz.; Yuma, Ariz.; Philadelphia, Pa.; Chicago, Ill.; St. Louis, Mo.; Cincinnati/Dayton, Ohio; New Orleans, La.; Little Rock, Ark.; Memphis, Tenn.; Shreveport/Monroe, La.; Lake Charles, La.; Jackson/Meridian, Miss.; Seattle, Wash.; Washington, DC; Minneapolis/St.Paul, Minn.

“Heat is a health hazard in many urban areas and the Heat Health Watch/Warning System provides heat information tailored specifically to your area,” said retired Air Force Brig. Gen. David L. Johnson, director of NOAA's National Weather Service. “People in certain cities are accustomed to a more temperate climate. When it gets unseasonably hot many people suffer, especially since many residences do not have air conditioning.”

"NOAA’s National Weather Service currently issues excessive heat products to provide the nation advance notice of excessive heat events for the protection of life and property," said Paul Stokols, NOAA National Weather Service health services program leader. "These products are based on a single heat index value derived from temperature and humidity. The Heat/Health Watch/Warning System is a custom made system developed for each urban area, based on specific meteorology for each locale, as well urban structure and demographics."

Philadelphia was the first city in the United States to implement the Heat Health Watch/Warning System program in 1997 and it has now become the worldwide model for heat forecasting. In fact, studies using three years of collected data indicate that 117 lives have been saved due to the Philadelphia heat program.

In the future, NOAA's National Weather Service plans to expand the number of Heat Health Watch/Warning Systems from the current 17 cities to each municipality with a population exceeding 500,000.

Preventing Heat-Related Illness
Although everyone is vulnerable to the dangers of extreme heat — elderly persons, small children, chronic invalids, those on certain medications or drugs (including tranquilizers and anticholinergics) and persons with weight and alcohol problems are particularly susceptible to heat reactions, especially during heat waves in areas where a moderate climate usually prevails.

Here are a few things you can do to protect yourself from the dangers of heat waves:

• Slow down. Strenuous activities should be reduced, eliminated or rescheduled to the coolest 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.
• Drink plenty of water or other non-alcohol fluids. Your body needs water to keep cool. Drink plenty of fluids even if you don’t feel thirsty. Persons who 1) have epilepsy or heart, kidney or liver disease, 2) are on fluid restrictive diets or 3) have a problem with fluid retention should consult a physician before increasing their consumption of fluids.
• Do not drink alcoholic beverages.
• Do not take salt tablets unless specified by a physician.
• 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.

Relevant Web Sites
NOAA National Weather Service

Heat Wave: A Major Summer Killer

NOAA's National Weather Service Heat Index

NOAA Heat Index Calculator

NOAA Heat Index Forecasts

SUMMER’S PEAK HAS ARRIVED - Caution: Deadly Heat Wave Reaches East Coast

U.S. EXPERIENCED RECORD WARM FIRST HALF OF YEAR, WIDESPREAD DROUGHT AND NORTHEAST RECORD RAINFALL

NOAA'S NATIONAL WEATHER SERVICE'S HEAT/HEALTH WATCH WARNING SYSTEM IMPROVING FORECASTS AND WARNINGS FOR EXCESSIVE HEAT: Excessive Heat Program Piloted in Philadelphia Is Becoming Worldwide Model

NOAA’S NATIONAL WEATHER SERVICE DEBUTS
HEAT HEALTH WATCH/WARNING SYSTEM IN PORTLAND METRO AREA

NOAA NATIONAL WEATHER SERVICE DEBUTS NEW HEAT/HEALTH WATCH WARNING SYSTEM IN THE SEATTLE AREA

NOAA UNVEILS NEW PROCESS TO HELP DETECT HEAT WAVES

HEAT WATCH/WARNING SYSTEMS SAVE LIVES: Estimated Costs and Benefits for Philadelphia 1995–98 BY KRISTIE L. EBI, THOMAS J. TEISBERG, LAURENCE S. KALKSTEIN,
LAWRENCE ROBINSON, AND RODNEY F. WEIHER

Media Contacts:
NOAA Weather Service Public Affairs, (301) 713-0622