How to Calculate Heat Index

Severe Thunderstorm Areas This Saturday; Excessive Heat in the Southern U.S.

Damaging thunderstorm winds and a few tornadoes with areas of excessive rainfall are possible today over parts of the lower Great Lakes to upper Ohio Valley and Mid-Atlantic, the Ozarks, and south-central High Plains. Excessive heat will continue over the southern U.S. this weekend before another round of heat arrives Monday through the central and southern U.S. spreading into the East by midweek. Read More >

Heat:

It's the number one weather-related killer in the United States. The National Weather Service statistical data shows that heat causes more fatalities per year than either floods, lightning, tornadoes or hurricanes. Based on the 10-year average from 2000 to 2009, excessive heat claims an average of 162 lives a year. By contrast, hurricanes killed 117; floods 65; tornadoes, 62; and lightning, 48.

The Heat Index is a measure of how hot it really feels when factoring in the relative humidity at a given location. While the all time high temperature in San Juan, PR soared to 98F on October 9th, 1981, Heat Index values across the Northeastern Caribbean often exceed 100 degrees on any given day. So if you think it feels hot outside, below are a pair of calculators that will allow you to calculate both the Relative Humidity and Heat Index at a given location if you know the temperature and dew point.