Water is refreshing in the heat, right? In parts of Florida this past week, not so much

Jul 13, 2023

The water temperature on the tip of Florida hit hot tub levels, exceeding 100 degrees (37.8 degrees Celsius) two days in a row. And meteorologists say that could potentially be the hottest seawater ever measured, although there are some issues with the reading.

KEY BISCAYNE, Fla. — In the sweltering summer heat, nobody tries to cool off by jumping into a hot tub. In parts of Florida, however, that's what the ocean has felt like.

Early last week, sea surface temperatures reached as high as 101.2 degrees Fahrenheit around the state's southern tip in Manatee Bay, according to the National Weather Service — although scientists said the context for the reading is complicated.

"It was like there was no difference between humidity of the air and going into the water," said Chelsea Ward of Fort Myers, Florida.

Triple-digit ocean temperatures are stunning even in Florida, where residents are used to the heat and where many retirees find refuge from cold, northern winters. Several other nearby spots reached the mid-90s. A storm came through Wednesday, helping water temperatures drop back down in to the more temperate 80s.

Humans naturally look to water for a chance to refresh. Every summer, millions grab their swimsuits for a day on the beach and a chance to cool off in the water — a break from everyday work and worry. Pools offer the same relief and a place for friends to gather. But when water temperatures get too high, some of the appeal is lost.

Beachgoers wade in the ocean Friday at Crandon Park in Key Biscayne, Fla.

Ward, 47, doesn't keep her beach bag in her car anymore even though she lives minutes away from the beach. Lately, the water is just too hot. Recently, when her friend asked if she wanted to go to the beach, the two decided against it after discovering the water temperature was around 90 F.

When it's hot, the body cools down by sweating, which evaporates and releases heat. Dipping into the ocean is typically so refreshing because heat efficiently transfers from your body into the water.

As water temperatures climb, that effect diminishes and you lose less heat less quickly, according to Michael Mullins, a Washington University toxicologist and emergency medicine physician at Barnes-Jewish Hospital in St. Louis.

A hot tub — or a stretch of ocean water hotter than body temperature — reverses the transfer of heat into your body. That's not a pleasant experience on a sizzling, humid, Florida day.

"It would feel," Mullins said, "like you are swimming in soup."

People already tend not to swim that much in the Florida waters that were so extremely hot. The water can get muddy and there are alligators and crocodiles in the area, too.

Still, high temperatures anywhere can make swimming less pleasant.

Graziano La Grasta, a contractor and standup paddle board enthusiast, rides a small wave Friday off South Beach in Miami Beach, Fla.

Through Friday, Phoenix endured highs above 110 F for 30 straight days. Pools are warm. About 150 miles to the northwest in Lake Havasu City, Arizona, Stefanee Lynn Thompson, 50, wanted to keep guests cool for a pool party she hosted. The heat raised the pool's temperature to 96 F.

Her friend recommended she go buy ice blocks. She ran to the grocery store, picked up 40 of them and dumped them in the pool. She set up fans, too. All that hard work dropped the pool's temperature a grand total of 4 degrees.

"When it's 120 out, anything helps," Thompson said.

Recently, ocean temperatures off the western coast of Florida have been a few degrees above normal, sitting around 88 to 90 F. It's not just humans that suffer when the oceans warm. Sea corals are bleaching. They can be hurt when water temperatures rise above the upper 80s.

July has been so hot that scientists announced a global heat record even before the month ended. Climate change is creating a hotter world, warming oceans and making some storms more destructive. Sea surface temperatures are somewhat above average around Florida, but they are far higher in parts of the North Atlantic near Newfoundland, where they are as much as 9 degrees hotter than usual.

The extremely high sea surface temperatures recorded in recent days off Florida's southern tip were caused by lots of sun, little wind and no storms.

"I've never seen temperatures 100 degrees in Florida Bay in the 21 years I've been in the Keys," said Andy Devanas, science officer at the National Weather Service in Key West, Florida.

Maria Argueta, 38, cools off Thursday with her son Matthew Pastrana, 2, and niece Aurora Reyes, 10, at the aquifer-fed Venetian Pool in Coral Gables, Fla.

There are some questions about how representative the 101.2-degree reading in Manatee Bay was. Water there is shallow and thus heats up quickly. If there's lots of sediment, that can raise temperatures, too, according to David Roth, a forecaster with the National Oceanic and Atmospheric Administration's Climate Prediction Center.

By contrast, stop by the YMCA pools in Massachusetts near Boston and you'll descend into water that's around 78 to 80 F. Sea surface temperatures off Cape Cod barely touched the mid-70s in recent days.

When Maria Argueta, 38, has time off from her job at an open-air decorative plant nursery in Homestead, Florida, she'll go with her family to swim.

The hot ocean water doesn't bother her, but sometimes she takes her 2-year-old son and other members of the family to the Venetian Pool, a public facility in Coral Gables fed by water from an aquifer that's always in the 70s. The very cool water, she said, is refreshing.

Florida's humid weather makes it harder for sweat to evaporate and cool down the body. People in south Florida know the ocean doesn't tend to offer real relief from that suffocating heat.

"You aren't getting much cooling at all," Roth said. "Nobody goes into the water in South Florida in the summer really except to swim, because it is comfortable to swim, but it is not refreshing."

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The water temperature on the tip of Florida hit hot tub levels, exceeding 100 degrees (37.8 degrees Celsius) two days in a row. And meteorolog…