With this year’s Atlantic hurricane season expected to be yet another stampede, Florida and other states around the Gulf of Mexico should keep an eye out for an underappreciated ingredient in the Gulf that can quickly turn storms into lethal monsters: hot ocean eddies.
Like hurricanes, the big ones even get names. Eddy Cardone, named for a pioneering meteorologist, has been swirling near the center of the Gulf since March.
“When storms encounter these puppies, they often explode,” said Nick Shay, a University of Miami oceanographer at the Rosenstiel School who’s studied currents and how ocean heat influences the atmosphere since the 1980s.
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The shallow swirls of warmer water occur across the planet near currents. In the Gulf, they spin off the Loop Current as it flushes hot water from the Caribbean and moves clockwise around the Gulf before flowing into the Florida Straits to join the larger Gulf Stream. The eddies can be more than 100 miles across and persist for months, Shay said, with several meandering around at the same time. When hurricanes encounter them, that warmer water can provide the energy a storm needs to intensify quickly.
Woods Hole, a private consulting firm that tracks eddies in the Gulf, has documented 78 since it began tracking them — and bestowing names — in the 1980s. In 2022, three appeared, including one named for Oscar Wilde that, like Dorian Gray, never seemed to die. It collapsed and reformed three more times.
Thanks to advances in ocean monitoring, Shay said scientists now know these eddies have been present when hurricanes rapidly intensify, going back to Hurricane Opal in 1995.
“It went to Cat 4 in 18 hours, and [forecasters] were all scratching their heads saying, what's going on here?” he said. “At that point the atmospheric scientists said, no, this is all atmosphere. It’s because this trough is coming in from the northwest. But we said, 'Oh no, no, no, no, no.' There was a warm core there and it provided higher octane fuel for that storm.”
Over the years, he said it happened repeatedly: with Gilbert in 1988, Lili in 2002, and Katrina and Rita in 2005. Hurricane Michael coasted over one when it became the first Category 5 storm to ever hit the U.S. mainland.
“This whole big blob of water is like a big, giant bathtub that's moving around and going very slow,” Shay said. “Back in 2021, Ida exploded. Again, it encountered that warm core eddy and, just like that, it went up to about a Category 4. So, again, it's not circumstantial.”
While they aren’t the sole cause for quick intensification, Shay said they can increase storm intensity by 20% to 40%.
Ocean currents play a significant part in regulating the planet’s temperature, carrying warmer water north. For decades, oceanographers have argued that currents, and not just the earth’s atmosphere, play a key role in hurricane strength. And as destructive as they are, hurricanes are also a way the earth releases heat.
But because eddies are so shallow — just a foot or so deep — Shay said forecasters doubted their power.
“The meteorological community was focusing in on, 'Yeah, but this is only 40cm high. How can it possibly affect hurricanes?'” he said. “It's not the vertical. It's the horizontal.”
As a hurricane moves across warm water, its winds typically stir up cooler water from the oceans, a process called upwelling. Temperature maps actually depict the wake left by that cooler water. But eddies do something peculiar when a storm crosses: they don’t mix because they contain so much heat, Shay said.
“Once you get strong winds, the mixing is going to kick in and it's going to start cooling the surface layer quickly,” he said. “That doesn't happen in an eddy. It doesn't significantly happen in an eddy at all.”
Scientists are now trying to better understand eddy dynamics and how currents shed them to better predict their formation ahead of hurricane season. The earth’s gravitational pull and latitude create a steady state not driven by winds currents. But add hurricanes — and things get mixed up. Rita proved that when it helped propel an eddy from the loop current. Monitoring can only detect them once they form.
Shay is part of a National Academies of Science study to better understand those dynamics. “For lack of a better word, it's completely nonlinear," Shay said. "In other words, it's very difficult to predict."
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