Blistering heat and triple-digit 'feels like' temperatures puts South Florida on high alert

A goopy exhale of super-heated air traveling from as far as Central America is smothering South Florida, triggering a rare multi-day heat advisory for a yawning area from Naples through West Palm Beach that warns of temperatures that could feel like 108 degrees.

The alert, which is in effect through Friday, is the first time since July 2020 that Palm Beach County was issued a heat advisory to alert residents that their natural cooling mechanism — sweat ― will falter in the high humidity.

The combination of high pressure in the upper reaches of the atmosphere, which dries up clouds and prevents widespread cooling rains, and a plume of warm moist air carried on southwest winds across the Gulf of Mexico is feeding the hot and soupy conditions.

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A heat advisory is issued for most areas when the heat index or “feels-like” temperature is expected to reach 108 degrees or higher for two hours or more. In Miami-Dade County, the National Weather Service issues a heat advisory if the heat index is expected to be 105 or higher for two hours or longer.

“With a high heat index, heat exhaustion and heat stroke can really sneak up on you faster than what you think,” said Adam Douty, a senior meteorologist for AccuWeather. “A lot of South Texas is very warm as well now, and that whole zone across the subtropics is pretty warm.”

Heat index meaning and how is it calculated?

The heat index is formulated with a punishing equation that considers the ambient temperature and amount of moisture in the air using the dew point or relative humidity. Dew point is the amount of water vapor in the air. Relative humidity is a percentage describing the amount of saturation of air.

For example, when the dew point and temperature are equal — as they nearly were early Wednesday when the air was 76 and the dew point 73 — the relative humidity is 100%.

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The wetter the air, the less sweat evaporates to cool you off.

Raquel Gobits, of Amsterdam, was in Palm Beach riding bikes with two friends when they stopped to take a swim at Midtown Beach. The trio, who are completing a hospitality industry internship in Fort Lauderdale, didn’t know about the heat advisory.

“We’re not used to this hotness,” Gobits said. “The bikes were a good idea at first, but now it is very hot.”

A lifeguard sign warning of hazardous conditions at the beach said "hot sand!!!"

There is also a measurement called the "wet bulb temperature" that considers even more ingredients when deciding what it actually feels like outside, including wind, sun angle, cloud cover and solar radiation. The wet bulb temperature incorporates a temperature reading taken in the sun, whereas the heat index uses a temperature taken in the shade to avoid interference from solar-heated surfaces, such as the metal of the instrument itself.

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Southern Florida heat wave consistent with rise in global temperatures

Florida Climatologist David Zierden said this week's heat is a singular weather event that can't be directly tied to climate change, although it is consistent with the rise in global temperatures.

"Over the past 10 years or so, we've seen a pretty dramatic rise in temperatures across the state of Florida, and that will lead to more extreme heat events," Zierden said. "Viewing it through that lens, there could be a relationship to climate change, but it's hard to pin that down to individual weather events."

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West Palm Beach is experiencing its second-hottest year on record with a mean temperature of 76 degrees through Tuesday, according to the Southeast Regional Climate Center. Fort Lauderdale, Miami, Fort Myers, Venice, Vero Beach and Melbourne all rank 2023 so far as their warmest year on record.

West Palm Beach nearly tied its record high temperature Tuesday, reaching 95 degrees at Palm Beach International Airport. While that was 1 degree shy of the 96-degree record set in 2011, it was still 7 degrees warmer than what’s normal for this time of year.

The normal high for West Palm Beach in mid-June is 88 to 89 degrees. The normal overnight low is 74 to 75.

“Seven degrees for South Florida is a lot,” Douty said. “Usually, your temperatures range within a couple of degrees every day, so when you get something like that, it’s a lot.”

Florida’s temperatures are moderated because it’s surrounded by water, which, especially in summer, keeps steep fluctuations at bay. But the same geographic positioning also makes Florida the most humid state in the country, according to a research paper Zierden co-authored.

Wednesday reached a high of 93 degrees in West Palm Beach, which is expected to be repeated Thursday. By Friday, that could increase to 95 degrees, but there are higher chances for afternoon thunderstorms that could cool the air down before sunset.

Kimberly Miller is a veteran journalist for The Palm Beach Post, part of the USA Today Network of Florida. She covers real estate and how growth affects South Florida's environment. Subscribe to The Dirt for a weekly real estate roundup. If you have news tips, please send them to kmiller@pbpost.com. Help support our local journalism, subscribe today. 

This article originally appeared on Palm Beach Post: Scary heat advisory for Palm Beach County and heat index meaning