Beware humidity in first heat wave of the season

Many people don't realize that heat is the number one weather fatality on a 30-year average - even more deadly than tornadoes and hurricanes - according to the U.S. Natural Hazard Statistics.

Posted 5:58 p.m. May 24, 2021 — Updated 6:27 p.m. May 24, 2021

Peta Sheerwood

, WRAL meteorologist

Many people don't realize that heat is the number one weather fatality on a 30-year average – even more deadly than tornadoes and hurricanes – according to the U.S. Natural Hazard Statistics.

Since we're tracking our first heat wave of the year, with a string of three or more days above 90 degrees, it's a good time to review life-saving measures and simple steps to avoid heat exhaustion.

A heat wave is typically sparked when heat and humidity ramp up with a high-pressure ridge over the southeast in the summer months, like what we have in place right now. Consecutive days with this kind of heat can have direct impacts on the body and heat- related illnesses can be avoided.

More 90s in store Thursday before cooldown comes for holiday weekend

The humidity can play be big role in how it feels outside, exacerbating stress on the body. The calculation of "feels-like temperature," also known as the heat index, factors the humidity and air temperature. For example, if the actual air temperature is 92° and the relative humidity is 70%, the heat index will be 112°. When relative humidity values increase, it is important to pay attention to how you feel when you are spending an extended period outside.

Evaporation is a cooling process. When we sweat, that is a form of evaporation. It is also the body’s way of removing heat. When humidity is low, drier air allows moisture to evaporate and efficiently promotes sweat which will cool the body. When humidity is higher, moist air limits evaporation. Ultimately, sweat evaporation will slow down and prevent the body from cooling off. An excess of this may lead to heat exhaustion and heat stroke.

Because impacts from the heat can turn fatal, the U.S. Occupational Safety and Health Administration (OSHA), athletic associations and the U.S. Army use the "wet-bulb temperature" product and guidelines to help them gauge how long to work outside and how many breaks to take from the heat. Unlike the heat index, the wet bulb temperature gives a measure of how it will feel in the shade. The wet bulb globe temperature is the measure of stress on humans and animals in direct sunlight. It takes into consideration the air temperature, humidity, cloud cover, wind speed and sun angle. This is also known as the heat exhaustion index.

There are simple steps you could take to avoid heat exhaustion. Never leave kids or pets in a closed parked vehicle. Drink plenty of water, even before you are thirsty. Breaks in the AC are essential. Limit strenuous activities outside. Stay in the shade. Wear light and loose clothing. If you plan to exercise outside, do it in the mornings or evenings when temperatures are not as hot the afternoons.

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