• After Hurricane Dorian made landfall in the Bahamas as a Category 5 storm, it slowed down and spent more than 24 hours pummeling the islands. Scientists call this “stalling.”
  • Hurricanes are carried by large-scale wind patterns, such as the trade winds. If those wind patterns dissipate, the hurricane stalls.
  • Hurricanes that stall are more damaging and they’re becoming more common, which scientists say may be linked to climate change.
  • There were 66 hurricanes that stalled in the North Atlantic between 1944 and 2017 and nearly half of those occurred in the last third of that time frame.
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Following is the transcript of the video.

Narrator: This is Hurricane Dorian on September 1, 2019. And here it is, more than 24 hours later. Still pummeling those same islands. [Pause] You see, Hurricane Dorian? It stalled … right there in its path. In fact, at times, it was crawling across the Bahamas at just 1.6 kilometers per hour! Slower than the average person walks. So, what causes hurricanes like Dorian to stall? And why does it matter?

First of all, Dorian is not the first hurricane to stall. Not even close, actually. In 2018, for example, Hurricane Florence spent more than 50 hours within one small region of North Carolina. And the year before, Harvey lingered over the Houston area for more than two days straight. But in every case, hurricanes that stall are really bad news.

Because the longer they linger the more rain they unload and the more damage they do. Harvey, for example, dropped more than 60 inches of rain in some parts of Texas. And it cost the country an estimated $125 billion. Dorian, on the other hand, dropped more than 36 inches of rain in some regions And is expected to have a multibillion-dollar price tag. So then, why do hurricanes stall?

Think of a hurricane like a cork bobbing in a stream. Although it produces its own wind and spin, it actually travels thanks to larger wind patterns. Which carry it along.

Timothy Hall, PhD: "And those wind patterns themselves evolve and change. And sometimes the winds that guide hurricanes collapse, and that's what you might think of as a "stagnation point."

Narrator: That's …

Hall: "Tim Hall. I'm a senior scientist at NASA Goddard Institute for Space Studies in New York."

Narrator: And he says that at these stagnation points, a hurricane has nowhere to go. So it just sits there, dropping rain, until another wind system picks it up and pushes it along. And that's exactly what happened in the Bahamas. When Dorian arrived, a pressure system nearby, called the North Atlantic subtropical ridge, started to weaken. And that caused winds that were carrying the hurricane to essentially stop blowing. And it will definitely happen again.

In fact, those stagnation events? They're actually becoming more common. And as a result, so are hurricanes that stall. According to Hall's research, there were 66 hurricanes that stalled in the North Atlantic between 1944 and 2017. And nearly half occurred in the last third of that time frame. Which helps explain another trend: The average speed o f hurricanes, in a given year, is declining.

In fact, compared to the mid-20th century, hurricanes today are moving, on average, about 17% slower! Now, scientists still aren't sure why, but…

Hall: "We've got some suspects, and the suspects are that in a warming climate, climate model simulations show, both in the future and in the past several decades, a reduction in the overall tropical wind patterns."

Narrator: And unfortunately, a stalled hurricane isn't the only consequence of climate change. It's also been shown to worsen storm surge. Increase rainfall. And produce more intense hurricanes. So, while Dorian is, of course, devastating. It's likely just one of many storms like it still to come.