After causing widespread flooding and knocking out power to half of Puerto Rico, the third hurricane of the season, Ernesto, has turned north and is now approaching Bermuda. In an average Atlantic hurricane season, the third hurricane doesn’t get going until September 7, so Ernesto arrived much, much earlier. By August 9, this summer had already produced a third of the activity of a typical season — and nearly 90 percent of that is still left.
All of that makes Ernesto, now a Category 2 hurricane, an ominous sign of what’s to come in the coming months — and what to expect as the planet rapidly warms. “For the third hurricane to arrive a little more than three weeks ahead of schedule is pretty impressive,” said Brian McNoldy, a hurricane researcher at the University of Miami.
This spring, scientists predicted the Atlantic would experience an exceptionally active hurricane season, with five major hurricanes and 21 named storms, and for one particularly good reason: The ocean is exceptionally warm and is expected to stay that way. In July, the temperature in the Atlantic hurricane hotbed was 2.8 degrees Fahrenheit warmer than the long-term average. “Hurricanes are like engines – they need some kind of fuel,” says Daniel Gilford, who studies hurricanes at Climate Central, a nonprofit research organization. “They need something to accelerate and pick up wind speed, and what they use to do that is primarily the ocean surface.”
As water evaporates from the ocean, floating clouds form, releasing heat and lowering air pressure. This sucks in air, creating winds and vortices. Hurricanes also love high humidity because dry air can slow the speed of the updrafts that storms need to grow big and strong. Hurricanes hate wind shear—winds that move at different speeds and in different directions at different altitudes. El Niño tends to encourage the spread of wind shear over the Atlantic, while La Niña tends to prevent them. Currently, conditions are “neutral” because El Niño has subsided and La Niña has not yet officially formed.
So high ocean temperatures aren’t the only ingredient for hurricane formation, but they’re certainly the fuel. As Ernesto chugged across the Atlantic between West Africa and the Caribbean, it encountered unusually high ocean temperatures that are at least 50 to 100 times more likely to occur with climate change, according to Climate Central’s analysis. (To be clear, this isn’t to say that Ernesto itself has become more likely with climate change—that requires further analysis.) Even more notably, the group found that Hurricane Beryl, a Category 5 that hit Texas in early July, was fueled by ocean temperatures that are made 100 to 400 times more likely with climate change. “We also know that storms are moving slower and lasting longer, and we expect those things to be affected by climate as well,” Gilford said.
High ocean temperatures also favor “rapid intensification” of hurricanes, defined as an increase in sustained wind speed of at least 35 miles per hour over a 24-hour period. Hurricane Beryl did this on its way to Texas, breaking records for the speed at which it developed into a monster storm. Rapid intensification makes hurricanes particularly dangerous, because a coastal city could be preparing for the landfall of a Category 2 hurricane, only to suddenly see a Category 5 hurricane. And the problem is getting worse, as research has found a dramatic increase in the number of rapid intensification events near the coast.
Fortunately for Bermuda, Ernesto has not increased in intensity as quickly — although it came close to doing so this week — but it is still a very dangerous Category 2 storm. “The shear may be a little stronger than originally thought,” says Samantha Nebylitsa, who studies hurricanes at the University of Miami, and “dry air has really hampered intensification. It just doesn’t let up.” That could well weaken the storm to a Category 1 by the time it reaches Bermuda.
The Atlantic will likely continue to provide more fuel toward the end of summer. Because the ocean takes longer to warm up than the land, hurricane season doesn’t peak until September. And the season doesn’t officially end until late November. “The best forecasts suggest we’re only maybe 15 or 20 percent through the total activity we expect for this year,” Gilford said. “There’s a lot more to come in 2024.”
