"Hurricane Laura’s rapid intensification is a sign of a warming climate." No shirt Sherlock.

The Washington Post

Climate and Environment

Hurricane Laura’s rapid intensification is a sign of a warming climate, scientists say

Hurricanes that go from dangerous to deadly very quickly are occurring more often, research suggests.

By Chris Mooney and Andrew Freedman

August 27, 2020

Surveying the Gulf of Mexico late Tuesday afternoon, National Hurricane Center experts saw a Category 1 hurricane — dangerous, but not likely to cause major damage. Forecaster Jack Beven put the storm’s maximum sustained wind speed at around 80 mph, forecasting a strong Category 2 storm by the next day.

Twenty-four hours later, Hurricane Laura was unrecognizable. It had rocketed into a high-end Category 4 storm, with wind speeds of nearly 145 mph, and was teetering toward Category 5 — the most dangerous.

It was one of the fastest transformations on record in the Gulf of Mexico.

Experts call the phenomenon “rapid intensification” and say it’s happening more frequently, thanks in part to warming ocean temperatures driven by climate change. The speed with which these storms morph can complicate both weather forecasting and emergency responses.

“Laura is, unfortunately, an example of the forecaster’s worst nightmare ... rapid intensification of a storm in the day or so leading up to landfall,” said MIT hurricane expert Kerry Emanuel.

Storms that quickly intensify close to land are not only likely to cause greater destruction, they allow little time for preparation — those in harm’s way may not see what’s coming.

“The problem is, several days out, people are tuning in, saying, ‘It’s a Cat 1, Cat 2, been through those, know what to do, not that bad,’ ” said Craig Fugate, who headed the Federal Emergency Management Agency during the Obama administration. “Then it starts intensifying and the window to evacuate closes very quickly.”

Research shows that rapid intensification events are getting more common in the Atlantic hurricane region as the climate warms. In fact, some experts say, it is almost as if as the maximum “speed limit” for storms increases, the storms themselves, like drivers, are adjusting by speeding up.

“A person coming off a stoplight in a 25-mph zone versus a 50-mph zone, you probably accelerate very differently in those situations,” said Gabriel Vecchi, a hurricane expert at Princeton University.

Laura ties the record

Jim Kossin, a researcher at the National Oceanic and Atmospheric Administration and the University of Wisconsin, says the warm ocean waters and exchange of heat between the ocean and atmosphere, plus the lack of dry air or strong upper-level winds, created an ideal environment for Hurricane Laura to rapidly intensify all the way to the Louisiana coastline.

Kossin said the unusually warm waters of the Gulf are tied in part to human-caused global warming, since the vast majority of the heat trapped in the atmosphere by greenhouse gas emissions ends up in the ocean.

With a 65 mph wind speed increase in 24 hours, Laura easily clears the threshold for a “rapid intensification” event by the National Hurricane Center’s standards. For the Gulf of Mexico, Laura’s intensification rate is only matched by 2010’s Hurricane Karl, according to Philip Klotzbach, an atmospheric scientist at Colorado State University. Storms in the Caribbean have intensified even faster.

But in recent years, other storms have also morphed quickly into major hurricanes, led by 2017’s Hurricane Maria, which managed an 80-mph increase in a day’s time and is blamed for the deaths of thousands in Puerto Rico.

The most rapidly intensifying storms have also usually been the most destructive — Harvey, Irma, Maria, Florence, Michael, Dorian and now Laura. And that’s just in the past four years. In 2005, the record intense Hurricane Wilma exploded by 110 mph in just a day.

What’s more, Hurricane Laura — like Category 5 Hurricane Michael in 2018 and Category 4 Hurricane Harvey in 2017 — intensified through the point of landfall, rather than weakening as they approached the Gulf Coast, which until recently had been more typical behavior, and which occurred with Hurricane Katrina in 2005.

Suzana Camargo, a research professor at Columbia University’s Lahmont-Doherty Earth Observatory, doubts a new trend of superstorms that don’t weaken near land. She said it’s more likely that storms that rapidly intensify tend not to follow the rules, period.

Scientists document the climate link

Increasingly, many scientists suspect climate change is playing a role in these events.

A 2019 study in the journal Nature documented a trend toward more rapidly intensifying hurricanes in the Atlantic Ocean between 1982 and 2009, and used a model that determined it would have been unlikely without human-caused climate change. Another 2020 study by Kossin and his colleagues further cemented the point by showing that globally, and especially in the Atlantic, storms are more likely now to reach the highest hurricane categories.

The strongest, most dangerous hurricanes are now far more likely because of climate change, study shows

“Our confidence continues to grow that storms have become stronger, and it is linked to climate change and they will continue to get stronger as the world continues to warm,” Kossin said.

As the planet heats up, warm tropical ocean water from the surface down to a depth of tens of meters or more provides energy for hurricanes. With more energy, the storm strengthens faster than it typically would.

Hurricane intensification right before landfall will be a growing risk as the planet warms, MIT’s Emanuel has warned.

But there is some debate over whether the dramatic changes in the Atlantic, particularly since the 1980s, are due chiefly to climate change or if atmospheric and oceanic cycles are also playing a role, Vecchi said.

Furthermore, some scientists think the reduction in sulfate aerosol pollution from power plants, thanks to the Clean Air Act, is also a factor in worsening hurricanes because the aerosols had a cooling effect by reflecting sunlight away from the planet.

The forecasting problem

Whatever is causing the changes, experts say that forecasting rapid intensification is difficult and it lags behind improvements in determining where storms will actually go.

“They’ve shown tremendous improvement in the track forecast, the intensity forecast is still an area that needs a lot of work,” Fugate said.

Hurricane Laura showcased the improvements made in forecasting a storm’s path. The National Hurricane Center accurately predicted the landfall location to within 0.6 miles, and at nearly the exact time of landfall, 87 hours in advance.

Still, even as the number of rapidly intensified storms increase, they remain relatively rare, Kossin said.

Most computer models that forecasters use don’t accurately capture rapid intensification events ahead of time.

“Forecasters are probably reluctant to go with a forecast of extreme, explosive intensification, you really go out on a limb there,” he said. “They just don’t have the guidance so they tend to be more conservative.”

While the official forecasts played catch-up with Laura, National Hurricane Center forecasters consistently warned in technical discussions read by meteorologists and emergency managers that the storm could become very intense and do so quickly. That way people paid close attention. “I think they did very well,” Camargo said. “They warned days before that there’s a chance it would become a very intense storm.”