What is the heat index?
Q: What is the heat index?
A: The heat index is a measurement that combines air temperature and relative humidity to give an equivalent temperature, or how hot it feels. It takes into account factors such as body mass, clothing, physical activity, sunlight exposure and wind speed.
Q: Who developed the heat index?
A: The heat index was developed in 1978 by George Winterling as the "humiture" and was adopted by the National Weather Service a year later. It is derived from work carried out by Robert G. Steadman.
Q: What is the difference between the heat index and humidex?
A: The humidex differs from the heat index in using the dew point rather than the relative humidity.
Q: When does the Heat Index agree with actual temperature?
A: At approximately 27 °C (80 °F), the heat index will agree with the actual temperature if the relative humidity is 45%, but at about 43°C (110°F), any relative-humidity reading above 17% will make the Heat Index higher than 43°C (110 °F).
Q: When are measurements taken for calculating Heat Index?
A: Measurements are taken based on subjective descriptions of how hot subjects feel for a given temperature and humidity, allowing an index to be made which relates one temperature and humidity combination to another at a higher temperature in drier air. The Heat Index is calculated only if actual temperatures are above 27 °C (80 °F), dew point temperatures greater than 12 °C (54 °F), and relative humidities higher than 40%.
Q: How should extra care be taken when outdoors during high temperatures?
A: When outdoors during high temperatures, measurements should be taken in shade instead of sun due to increased UV radiation exposure, so extra care must be taken while in direct sunlight.
