Thursday, December 3, 2020
Dec. 3, 2020

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Climate change may affect storms’ ‘rapid intensification’


When Hurricane Laura battered Louisiana in August, becoming the most powerful storm to ever make landfall in the U.S., forecasters were confounded by its behavior.

Not only did it fail to lose power as hurricanes often do when they approach land, it appeared to be doing the exact opposite, exploding from a Category 1 to a Category 4 storm in less than 24 hours. By the time it made landfall, Laura’s winds were clocking 150 miles per hour. Projected storm surge jumped from 11 feet to 20 feet, and Louisianans intent on riding out a weaker storm were forced to make an 11th-hour decision to evacuate.

Laura’s behavior, known as rapid intensification, was likely exacerbated by climate change, according to some scientists, with warmer ocean waters causing storms to become supercharged. Meteorologists can’t yet predict which hurricanes will become overnight monsters, but as the waters of the Gulf of Mexico and along the Atlantic Coast continue to warm, residents there will likely face more volatility, which means greater danger.

“It can create big problems for preparations,” said Chris Davis, a hurricane scientist at the National Center for Atmospheric Research. “People might decide not to evacuate for a Cat 1 and by the time it is clear that the storm will be more intense, it is too late to change plans.”

The National Hurricane Center defines rapid intensification as an increase in storm winds by about 35 miles per hour in 24 hours, said Dennis Feltgen, spokesman for the agency. In 2020, nine storms have rapidly intensified ahead of U.S. landfall: Hanna, Laura, Sally, Teddy, Gamma, Delta, Epsilon, Zeta, and Eta. Two of the most devastating storms to slam American shores in recent years — Hurricane Harvey in 2017 and Hurricane Michael in 2018 — both gained strength as they approached land.

“Rapid intensification is nature’s turbo-boost button for hurricanes and can produce a hurricane on steroids within a matter of hours,” said Andreas Muehlbauer, an atmospheric scientist at commercial insurer FM Global.

It’s not a new phenomenon, but it may become more frequent if the world keeps warming. In simulations, storms gaining 69 mph in the day before landfall used to happen only once every 100 years, according to a 2017 paper by Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology, published in the Bulletin of the American Meteorological Society.

But in simulations using a warmer, late-21st century climate, these monster storms can occur every five to 10 years. As the climate continues to warm, the likelihood of more storms undergoing an explosion of power will rise, Emanuel wrote.

Explaining how and why that happens could save lives. About 56 percent of all U.S. storm-related fatalities since 1900 have come from just three storms, according to Emanuel. Hurricanes that quickly gain power are more likely to catch people unawares, with catastrophic consequences.

In September 2015, the crew of a cargo ship called El Faro set out to sea near Bermuda, believing that it could slip around a weak tropical storm. But within 24 hours the tropical storm had turned into a Category 4 monster with winds of 155 miles per hour. The ship sank, killing its crew of 33.

The process is probably being fueled by warmer Atlantic waters, said Dan Kottlowski, a meteorologist with AccuWeather Inc. Some point to the Atlantic Multidecadal Oscillation — a theory that the ocean undergoes decadelong sweeps between being warmer and cooler — as one cause for rising sea temperatures, but Kottlowski is convinced climate change has a role.

The exact causes of intensification are difficult to root out without more information about what’s happening inside a storm between the ocean and the clouds. The problem is that, once a storm starts to strengthen, that layer becomes one of the most dangerous places on Earth. High waves and thrashing winds all make it difficult for meteorologists to get airplanes and equipment into the area to find out what’s going on. Without those measurements, “all these models we use to predict intensity have limitations,” Davis said.