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The Rapid Intensification of Hurricane Lee Is a Warning [1]

['Condé Nast', 'Matt Simon', 'Amanda Hoover', 'Will Bedingfield', 'Adrienne So', 'Alex Christian', 'Roger Highfield', 'Celia Ford', 'Rachel Nuwer', 'Max G. Levy']

Date: 2023-09-08 15:40:21.210000+00:00

But a hurricane also needs humidity: If it runs into dry air, that can actually counteract warm waters, to a certain degree. “If it’s dry enough, you get really rapid cooling because of the evaporation, and you get downdrafts—that cooler air wants to sink,” says Dunion. “Downdrafts are just not what a hurricane wants to see if it wants to intensify. It’s all about the updraft.”

Due to climate change, some parts of the world are indeed getting more humid as higher temperatures evaporate more water off the ocean surface. Generally speaking, a warmer atmosphere can also hold more water vapor than a cooler one: For every 1 degree Celsius of warming, you get 7 percent more moisture in the atmosphere. The oceans have also absorbed 90 percent of the additional heat that humanity has added to the atmosphere, providing all the more energy to supercharge hurricanes.

Today, Dunion’s team is flying out to Lee in a research aircraft that will parachute instruments into the storm to measure its humidity, along with wind speed, temperature, and pressure. They’ll also fly a drone closer to the ocean surface to measure how energy is being exchanged between the sea and the storm. “It’s really important to know while this storm is rapidly intensifying: How is that affecting the winds down at the surface? How quickly do the winds down at the surface respond to this rapid intensification?” asks Dunion. “That’s all important to the forecast.”

Another key variable in rapid intensification is land. Part of what has made Lee grow so strong is that it’s a “Cape Verde hurricane.” These form off the coast of Africa and head toward the Americas, feeding for thousands of miles on warm Atlantic waters—a constant source of energy, as these hurricanes don’t hit land until they cross the whole ocean. Once they do reach land, storms lose that source of energy. Mountains in particular can slice through such storms, weakening them. That’s why hurricanes lose strength as they travel through Southern states like Louisiana: Deprived of fuel, their winds peter out and they dump out their moisture as rain.

Hurricanes also hate vertical wind shear—basically, differences in wind speed and direction at different altitudes. “If [winds are] too different, it’s almost like tipping a skateboarder over—the storm starts to get tilted and not really be able to strengthen,” Dunion says. Interestingly enough, early this summer, before hurricane season got going, scientists were speculating about whether El Niño might butt in and help break up this summer’s storms. That’s because El Niño—a band of warm water in the Pacific—tends to create wind shear in the Atlantic. But clearly, Lee doesn’t seem fazed.

Putting it all together: To get rapid intensification, you need warm water, high humidity, and low wind shear. If you knock out any one of those variables, it’s a no-go. That’s what makes rapid intensification very rare. And even with all those variables lined up, rapid intensification isn’t a sure thing. “We don't have a deep understanding of the reason why we have this rapid intensification,” says University of Delaware atmospheric scientist Shuai Wang. “We can say: OK, now we have a high probability to have such events, but we are not sure whether or not it will happen.”

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[1] Url: https://www.wired.com/story/the-rapid-intensification-of-hurricane-lee-is-a-warning/

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