Hurricanes that stall are becoming more common. They can dump more rain than a faster-moving hurricane and often follow a less predictable path.
Dorian is just the latest example. One study found that over the past 70 years Atlantic hurricanes have gotten more likely to stall.
“We've seen about a 60 percent increase in the frequency of events like Dorian stalling near the coast,” said Timothy Hall, a senior scientist at NASA Goddard Institute for Space Studies and an author on the study. “The culprit is related to a slowdown in large scale atmospheric wind patterns likely due to a warming climate.”
Hurricanes have high wind speeds internally, but they don’t necessarily move from place to place very quickly.
Wind patterns in the subtropics appear to be slowing down and climate change simulations predict exactly this phenomenon.
Hurricanes are responding to that, he said.
“Hurricanes are kind of like corks on a stream,” Hall said. “Imagine a cork moving into an eddy.”
The signal is “noisy,” Hall said, but the cutting edge of research is pointing to a relationship between climate change and stalling.
Hall warned that this is the “least well-understood” of the relationships between hurricanes and climate change.
The best-understood relationship is the fact that sea level is rising and that causes higher storm surge when hurricanes hit.
Also well-understood: hurricanes will dump more rain because of warming sea temperatures.
“That's simply because warmer air and a warmer climate holds more water in vapor form,” he said.
Hall explained that the climate models do not predict more hurricanes, but they do predict higher wind speeds and more rain, as seen in recent years with Hurricane Florence (2018) and Hurricane Harvey (2017).
“Unfortunately, I'm the bringer of bad news,” he said. “The long-term trend appears to be clear.”