Weather Workshop: Heat Index

Weather Workshop: Heat Index
The heat index is used to tell us how hot it feels outside but how is it calculated? (Source: WMBF)

MYRTLE BEACH, SC (WMBF) - It’s the dog days of summer and you’re hearing phrases like “feels-like” or “heat index”. Living in the south, we understand how the heat and humidity operates here in the Carolinas. Our daily forecast includes the muggy meter or heat index daily. It’s a term that most people understand the concept but don’t fully understand how it’s found.

The heat index is talked about a lot but here is how it's calculated.
The heat index is talked about a lot but here is how it's calculated. (Source: NOAA)

The Heat Index is a measure of how hot it really feels when the relative humidity is factored in with the actual air temperature. To find the Heat Index or Feels Like Temperature, you can use a simple chart that the National Weather Service uses. For example, if the air temperature is 98° and the relative humidity is 60%, the heat index is 123°.

Relative humidity simply tells us how much water is in the air. Your relative humidity is usually highest in the overnight and morning hours when the temperature and dew point is closer. However, your heat index is usually the highest when you have the warmer temperatures with decent relative humidity values.

Here’s a quick example of how that happens using the heat index calculator.


Temperature: 79°

Relative Humidity: 95%

Heat Index: 83°


Temperature: 95°

Relative Humidity: 65%

Heat Index: 118°

Now it’s your turn! Set your temperature to 75° for the morning with a relative humidity of 95%. You should get an answer of 77° for the heat index.

1) As you raise your temperature five degrees, how quickly down the heat index climb? When does it hit triple digits?

2) Can you find a temperature with a relative humidity of 65% that will equal 93° for the heat index? If so, what is it?

3) What about setting your relative humidity to 80%? Can you find a temperature that will equal a 125° heat index?

Send your answers to @AndrewWMBF or @JessicaDobsonWx or Twitter. You can also send a message with your answers to Andrew or Jessica. Let’s see if you can get it right.

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