JACKSONVILLE, Fla. — Heat Index is a great tool to gauge "how hot it actually feels outside" when you combine the temperature and relative humidity outside. What folks might not realize is Heat Index is measured in the shade. There are other factors like wind speed, sun angle, and solar radiation or cloud cover to take into consideration.
That's where Wet Bulb Globe Temperature (WBGT) comes into play. It might not be as well known to some, but it's been used for decades. Developed in the 1950s, the WBGT has been used by military agencies, OSHA, and even marathon organizers. If you work or exercise in direct sunlight, this is a good element to monitor.
WBGT can be confusing to some because it has a different scale when compared side by side with Heat Index.
For example, on a summer afternoon in late July with a forecast high of 97F, a dew point of 76F, and a calm southwest breeze, the Heat Index could be up to 111F while the WBGT could be 90F. According to the National Weather Service, a WBGT of 90 would mean working or exercising in direct sunlight will stress your body after just 20 minutes. The suggested action for heat illness prevention would be to take at least 40 minutes of breaks each hour.
Naval Station Mayport posted to their Facebook page about Wet Bulbs on Monday, August 2 suspending physical training and strenuous exercise for all personnel.
Bottom line: Heat Index is more conversational and easy to digest, while it might take a minute to remember the scale for WBGTs. However, they both are a good tool when determining how intense the heat and humidity is during the summer months!