NASHVILLE, Tenn. (WKRN) — For the first time since last fall, Middle Tennessee will see three consecutive days in the 90s. Does this count as a heat wave, or is this normal for this time of year?

According to the National Weather Service office in New York City, a heat wave is defined as three consecutive days of 90° or higher.

The News 2 Weather Authority team is forecasting temperatures of 90° or higher from Tuesday, June 3, through Thursday, June 5.

This would meet the National Weather Service New York City's office definition for a heat wave. New York is not Tennessee, so is the definition of a heat wave different here in the Volunteer State?

According to Nashville National Weather Service meteorologist Ryan Husted, a heat wave is a prolonged period of abnormally hot weather. This means the criteria for a heat wave in New York City would not work here in Middle Tennessee. This is because temperatures in the 90s are not abnormal.

The average high temperatures in Nashville are 90° or higher from June 25 through August 26. This is more than two months where 90° is normal.

Husted said in Middle Tennessee, abnormally hot conditions are when the heat index gets above 105°.

"For us, 90s in June is not abnormally hot. Now, if we have those temperatures approaching 100°, and if we have that humidity, those dew points of 75° or 80° with a temperature of 95°, making it uncomfortable, that's what we would constitute a heat wave," Husted told News 2.

The heat index, or feels-like temperature, is how hot it feels to a human. It takes into account the moisture in the air along with the temperature. This is because it feels much hotter when there is more moisture in the air. Below is a heat index chart that has the temperature on the y-axis and dew point on the x-axis.

The National Weather Service office in Nashville will issue heat advisories when the heat index is higher than 105° and extreme heat warnings when it gets above 110°. The criteria for heat alerts across the United States are based on feels-like temperatures that are abnormally or dangerously hot.

This means a heat wave in Middle Tennessee would be at least three days when the heat index is 105° or warmer.

Husted said this warm-up is not abnormal enough to be a heat wave, but it could be a shock to your system since it's been so cool lately.

"By the technical definition, we currently don't meet the criteria for this upcoming event, but that's not to diminish the potential impacts. It's our first heat event of the year, we're not used to it at this point," Said Husted.

News Source : https://www.wkrn.com/news/local-news/nashville/will-middle-tn-experience-a-heat-wave-this-week/