It’s hot in Florida. Shocking news, right? In a state where temperatures can easily top 90 from April to October, how a heat wave is defined may surprise you. Many Floridians are experiencing one this week.

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The Definition Depends

The National Weather Service defines a heat wave as “a period of abnormally and uncomfortably hot and/or humid weather typically lasting two or more days”. The threshold of temperature (or heat index) varies by region, though.

Meteorologist Daniel Noah from the National Weather Service in Tampa says the official weather service alerts are based on the outcomes of prior excessive heat events.

“The criteria for a Heat Advisory was developed by looking at the number of admittance into local emergency rooms due to heat.”

When an apparent temperature - what the humidity can make it feel like to your skin - is expected to reach 108° over a large area, the advisory is usually issued before sunrise. When those numbers hit 113°, the advisory is upgraded to an Excessive Heat Warning. This benchmark applies to the entire state.

Earlier this year, Doctor Emily Leary, Assistant Research Professor at the University of Missouri School of Medicine, developed a new formula for determining how a heat wave is defined.

“Having a heat wave definition that includes localized information is important, because then that heat wave reflects what is actually happening in that area.”

Dr. Leary’s approach is based on location, what is normal for that location, at a particular time of year. In Pensacola, for example, a heat index in July above 110° for a period of three straight days would be considered a heat wave. This number would not be as high in a city that has a lower mean temperature or experiences less annual variability.

The challenge with her formula is that the data isn't always available.

“Looking at missing data in important, because those affect the climate norms that are calculated for an area, and those affect heat wave definitions and other measures.”

Dr. Leary also noted that in some cases, particularly in Florida, “extremes are sometime felt by the public before the National Weather Service advisories are put out.”


When Hot is Too Hot

Excessive heat can be deadly. According to NOAA, more than 100 fatalities per year are attributed to a heat-related illness in the United States. These numbers can spike during an extreme event such as the Chicago Heat Wave of 1995, when more than 700 residents died during a four-day span of triple-digit heat in July.




John-Michael Gonzales is a communication specialist from the Florida Department of Health. He says that just because we’re acclimated to the heat doesn’t make us immune to its hazards.

“I know a lot of florida residents think that they’re used to it, but when we have these spikes, a lot of folks who think they can handle the heat might not take the necessary precautions.”

John-Michael noted that drinking lots of water - even if we're not thirsty - is the first step to keeping the heat from being harmful. And if we don’t, heat exhaustion could set in.

“Things to specifically look out for are dizziness or lightheadedness, bad headache, or nausea. If you experience these things, you should take a break and immediately get out of the sun if you can.”

Mr. Gonzales says if those symptoms continue, heat stroke could occur, which is fatal if not treated right away.

According to the Center for Disease Control and Prevention, in addition to young children, the elderly, people who have a low income, chronic medical conditions, or must work outdoors are more at risk to the dangerous heat.

The Hottest State

Triple-digit temperatures are not as common as one might think in Florida. For example, Jacksonville only averages one per year, whereas the mercury climbs above 100° an average of 16 times in Dallas, a city roughly about the same distance from the equator.  However, during the span of an entire year, Florida is the warmest state in the U.S.

The moderating influences of the Atlantic Ocean and Gulf of Mexico play a role in keeping daytime temperatures in check during the summer. Sea breeze boundaries, acting as miniature cold fronts, work their way inland and provide relief in the way of afternoon thunderstorms or cloud cover. This is why temperatures are often much warmer over inland areas where that cooler ocean air is delayed, or sometimes never makes it.

Conversely, the presence of a wind off the water at night, can lead to extremely warm overnight low temperatures. In some cases, immediately near the water, the mercury will never fall below 80° in the summer months. Water heats and cools at a much slower pace than land, which explains the opposing trends.

Florida’s humidity, to no surprise of many, is the real factor. It can sometimes add more than ten degrees to what your body feels. This is important, because the apparent temperature is what your body is forced to fight when it gets overheated.


Hot and Getting Hotter

According to the Florida Climate Center, June was warmer than normal in all 67 counties of the state. Several cities, including Miami and Tampa, had average monthly temperatures place in the top ten on record. And just like every other state in the country, July is Florida’s hottest month of the year. Right on cue, temperatures are on the rise this week.



Above normal temperatures and below normal rain chances are both expected across Florida over the next 6 to 10 days. In the more immediate future, afternoon highs are projected to approach the century mark near the Georgia border, and the heat index will be well into the 100's for several hours across nearly the entire state over the next several afternoons.

A strong ridge of high pressure, one that is typically more centered to the east of Florida, is parked over the Sunshine State and expected to remain there for many days. Only a strong front from the north, or possibly a tropical wave moving in from the Caribbean will be able to weaken this weather system and squelch the heat. Some relief, mainly in the form of a few more afternoon thunderstorms and clouds, is forecast to arrive by early next week. However, a significant cool down is not anticipated through the middle of July.




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