Hurricanes and typhoons are slowing down, troubling new study finds

Hurricanes and typhoons — the monstrous, destructive storms that bring extreme wind and rain to coasts around the world — are slowing their pace as they traverse the globe. 

After assessing every tropical cyclone on record between 1949 and 2016, National Oceanic and Atmospheric Administration (NOAA) scientist James Kossin found that the storms have slowed down in every ocean, save the Northern Indian. 

This research, published Wednesday in the journal Nature, concluded these storms are now moving about 10 percent slower on average than they did in the past, though regional speeds in specific oceans vary. 

At first blush, 10 percent might sound like a relatively small percentage, but in reality, it’s a big deal, said Kossin, in an interview. A storm that sits still over one place for an extended period of time brings that much more wind and rain to that area.

“Nothing good can come of a slower storm,” said Kossin. 

Hurricane Harvey on August 25, 2017, when it reached maximum sustained winds of 130 mph.

Hurricanes already bring a number of well-known hazards — flooding, pummeling winds, and surging seas — all which can prove fatal and wreak havoc on infrastructure. 

In a May 2018 report, NOAA said last year’s Hurricane Harvey, which stalled over Houston, was responsible for the direct deaths of at least 68 Americans. 

“It’s safe to say you want them [hurricanes] to get out of your neighborhood as quickly as possible,” said Kossin.

Hurricane Harvey may have been exceptional — breaking rainfall records while dumping over four feet of rain onto Houston — but any cyclone can wreak havoc if slowed or stalled. 

“Sitting still for two days is a big deal,” Hugh Willoughby, a hurricane researcher at Florida International University who had no role in the study, said in an interview. 

Willoughby noted that there’s another culprit at play here, too. With every 1 degree Celsius (1.8 Fahrenheit) rise in global temperature, the atmosphere becomes capable of holding 7 percent more water vapor, which provides fuel for heavier downpours. 

A Houston resident paddles through his home following Hurricane Harvey.

“This research gives a pretty good picture of what we should expect in the future,” said Willoughby. “The threat to the U.S. is from flooding.”

Atmospheric scientists, like Kossin, have a pretty good idea about why these storms are slowing down as well. 

Warming global temperatures, especially the accelerated heating of the Arctic, are disrupting the way air travels through the atmosphere. 

One of these changes amount to a weakening circulation of tropical air, particularly during the summer. These winds, and others, are hugely influential as they push major storms around “a bit like a cork in a stream,” said Kossin.

“It makes physical sense that they should be slowing down,” said Willoughby, adding that there’s still not quite enough historical storm data to say for certain that the storms have slowed as much as the new study shows. 

“Stuff happened out in the ocean before 1950 that we didn’t know about,” said Willoughby.

Today, NOAA has a sophisticated group of weather-tracking satellites, so in the coming years scientists’ grasp of storm trends will only improve. But at the same time, global temperatures will almost certainly increase, perhaps by 6 degrees Fahrenheit by the end of the century if the global community fails to rein in carbon emissions. 

Damage to U.S. communities and coastlines from future hurricanes are expected to hit the U.S. economy quite hard. Research published in the journal Environmental Research Letters found that future storms — enhanced by rising seas and carrying more water — could bring three times the amount of economic damage than infrastructure-pummeling tempests do today.

Over the nearly 70 years of hurricane data Kossin analyzed, the planet warmed by half a degree Celsius (about 1 degree Fahrenheit) on average, but it’s unknown what will happen with another degree of warming or more, said Kossin. There could be more than a 10 percent drop in storm speed — or perhaps less.

What is known, however, is that while deaths from surging stormwaters on U.S. coastlines have gone down over the decades, inland flooding has become a substantially higher risk for death, said Kossin. People generally don’t evacuate from these places during hurricanes, said Kossin.

“That’s a scary idea,” he said.