Heat index: What is it and why is it different from the actual temperature

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TAMPA, Fla. (WFLA) – The heat index is the temperature that it feels like to our skin when relative humidity is factored in with the actual air temperature.

The heat index, or the “feels like” temperature, differs from the actual air temperature when the humidity levels are very high or very low and can be very dangerous.

Heat exhaustion or heat stroke can result from prolonged periods outdoors in triple digit heat indices because the body feels hotter and loses its natural ability to cool down.

As the air temperatures rises, the body begins to sweat and most days the sweat will evaporate. Sweating is the body’s natural way of cooling down because evaporation is a cooling process. As the sweat droplets evaporate off the surface of the skin, it leaves the skin feeling cooler.

When the humidity levels are high, the extra moisture makes it harder for the sweat to evaporate. Slower evaporation leads to the sweat lingering on the skin and the body not being able to properly cool down. This leads to the body feeling hotter, hence the “feels like” temperature.

Heat advisories are issued in Tampa when the heat index is forecast to be above 108 degrees. It is important to note that most heat indices are given for what it will fee like in the shade. In the sun, the heat index could go up by 15 degrees.


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