Earlier this week, mission control commanded the International Space Station to turn its cameras toward the Gulf of Mexico. Giant white clouds, gleaming against the blue of the planet’s oceans and the blackness of space beyond, indicated the arrival of Hurricane Idalia, hovering menacingly off the coast of Florida. From that high-flying view, you couldn’t tell exactly how much havoc Idalia would wreak—the record-breaking storm surges; the flooding across Florida, Georgia, and the Carolinas—or the very unusual conditions in which the storm had formed.
This hurricane season has been a weird one, because two opposing trends are driving storm dynamics. The planet is in an El Niño year, a natural, periodic climate phenomenon that tends to suppress hurricane activity in the Atlantic basin. The Atlantic hurricane season has been fairly quiet this year, in part because of these conditions.
But we’re also in a very hot year, on track to becoming the warmest on record. Earth’s oceans have been warmer this summer than at any other time in modern history. The Gulf of Mexico has been particularly hot; climate experts have described recent temperatures there as “surreal.” Global temperatures are usually higher during El Niño events, but “all of these marine heat waves are made warmer because of climate change,” Dillon Amaya, a research scientist at the National Oceanic and Atmospheric Administration’s Physical Sciences Laboratory, told me earlier this summer. And hot seawater tends to supercharge hurricanes that do form by warming up the air above the ocean’s surface.
We’ve never seen a year quite like this, with its particular mix of extreme ocean temperatures and El Niño conditions—which means no one knew exactly how bad this season’s storms could be. In the case of Hurricane Idalia, the warmer temperatures seem to have won out. Idalia feasted on the abundant supply of hot air to jump from Category 1 to Category 4 in just a single day. Climate experts caution that we can’t use the story of one hurricane to fill out the narrative of an entire season. But climate change has warmed our oceans, and warmer oceans make hurricanes more likely to intensify rapidly and become powerful storms in a matter of hours rather than days. Now, with Idalia, we have a clear example of what can happen when that reality is paired with superhot oceans.
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Under more normal ocean conditions, a hurricane can derive only so much fuel from hot water. The toasty air on the surface fuels the winds, and “the motion of the winds themselves churn up the water," which brings cooler water from the depths up toward the surface, Kim Wood, a professor of hydrology and atmospheric sciences at the University of Arizona, told me. The process is called upwelling. But when warm water stretches deep into the ocean, the cool stuff never rises to the top. The winds end up “just bringing more warm water to the surface—and thus continuing to provide energy to the storm,” Wood said.
Hot water, of course, is not the only condition required for a hurricane to form. Many other factors drove Idalia’s intensity, including the behavior of winds in the upper atmosphere, and the structure of the storm itself. "Any particular storm is influenced by a lot of different things, a lot of which can be racked up to chance," Kerry Emanuel, a meteorology professor at MIT, told me. Still, ocean temperatures certainly helped Idalia’s winds reach 125 miles an hour, and potentially increased its intensity by at least 40 to 50 percent, according to the hurricane scientist Jeff Masters.
Around the world, the frequency of rapidly intensifying storms near coastlines has tripled compared with 40 years ago, according to a recent study. Space imagery this week showed another swirling beast in the Atlantic: Franklin, a hurricane that had also exhibited signs of rapid intensification, which means that a storm's top wind speed has increased by at least 35 miles an hour over 24 hours. (According to the meteorologist Philip Klotzbach, the Atlantic Ocean had not seen two hurricanes with 110-plus-mile-per-hour winds at the same time in more than 70 years.) “We don’t understand the physics related to the rapid intensification well at the moment,” Shuai Wang, a meteorology and climate-science professor at the University of Delaware, told me. That unpredictability makes preparedness much more difficult, he said. Government agencies and citizens alike might be planning for one kind of storm, only for it to quickly turn into something very different.
[Read: We’re gambling with the only good oceans in the universe]
Idalia, now a weaker tropical storm, is currently dumping rain on North Carolina as it moves back out to sea. The former hurricane may or may not be a sign of what’s to come for the rest of this hurricane season. The Atlantic Ocean is expected to stay warm through the end of the season, in November, so potential storms will encounter more fuel than usual. But forecasts for the season have been uncertain because there’s not much precedent for the current situation.
“We have El Niño pushing us to maybe think that we have a below-normal season, but then the very, very warm tropical Atlantic is pushing us to think maybe there would be an above-normal season,” Allison Wing, a professor of Earth, ocean, and atmospheric science at Florida State University, told me. “For the hurricane season overall, I think we don’t know yet which one wins at the end.”
There are some things we can say with more certainty about our hurricane future in a hot world. Rising seas and record-breaking air temperatures have made hurricanes wetter. “If the air in which the hurricane is occurring is warmer, it’s going to rain more,” Emanuel said. “The same storm is going to have surge riding on an elevated sea level.” That’s a scary prospect for a world in which the air is getting warmer and sea levels are rising—especially because flooding poses more peril than wind. “Wind is what we think of; it’s what we measure; it’s what we report,” Emanuel said. “But water is the killer.”