Hurricane Dorian dumped more than 36 inches of rain as of Wednesday morning on the Bahamas as it hovered over the islands for more than two days, causing dangerous flooding and trapping some people in their homes. For the Bahamas, where at least 30 people have died, “the devastation is unprecedented,” Prime Minister Hubert Minnis said on Monday.
But the basic conditions of the disaster — a stalled hurricane and its sopping aftermath — are not one-off events.
Over the last seven decades, hurricane stalling, which causes a storm to release massive amounts of rain on small areas, has become more common, research published in June in the journal Nature shows. But it is currently unclear if the trend is due to climate change or natural variation.
By studying hurricanes from 1948 to 2017, researchers found hurricanes are slower than in the past and are more likely to sit over a region for 48 hours or more. The longer a hurricane stalls, the more rain it pours on that area.
Tim Hall, a senior scientist at the NASA Goddard Institute for Space Studies and co-author of the report, said Hurricane Dorian is a “classic example of an extreme stalling event.”
Dorian was on track to move through the Bahamas and hit the southern coast of Florida. But then it seemed to pause, wreaking havoc on the islands. Now, it has turned northeast, heading up along the coast of the U.S. mainland.
To explain the shift, Hall likens hurricanes to a cork in a river. The storms don’t produce any directional force to move themselves. Instead, they are pushed around the ocean by wind streams, which are caused by high and low pressure systems in the atmosphere.
Occasionally, the winds die down or push against each other in such a way that the hurricane gets stuck — much like a cork might in an eddy — until the winds change and push it along.
“In the case of Dorian, it just so happened that in the Bahamas, and near the coast of Florida, these large-scale pressure systems were changing. The steering winds collapsed, and Dorian stagnated,” Hall said.
While over the Bahamas, Dorian was moving at as little as 1 mile per hour.
“It’s bad enough to get hit by a [Category] 5 hurricane. It’s even worse to have it sit there,” Ken Graham, director of the National Hurricane Center, told the PBS NewsHour on Tuesday. “It’s just a devastating situation for the Bahamas,” he added.
Other recent examples of stagnant hurricanes include Hurricane Harvey over Houston, Texas, in 2017, Hurricane Florence in 2018 over the Carolinas and Cyclone Idai in Mozambique earlier this year.
What could be causing hurricanes to stall
The connection between hurricane stalling and climate change is still being studied, but there is a hypothesis being explored about the increased frequency.
Typically, winds are created because the Earth’s poles are much colder than the tropics around the equator.
“The way the planet deals with that imbalance is to move [the energy] around” through winds and ocean currents, said Jim Kossin, Hall’s co-author and an atmospheric research scientist at the National Oceanic and Atmospheric Administration.
Global warming is causing the poles to heat up, reducing the need to exchange so much energy between the poles and the tropics.
While the connection needs more data collected over time , Kossin warns that “we shouldn’t wait until we are absolutely sure” before taking significant steps to combat climate change, which has already been proven to make hurricanes stronger and more dangerous.
What this means for hurricane preparedness
In general, global warming and climate change are key factors in why hurricanes are becoming more damaging.
Increased sea level rise — due to melting glaciers and heat-driven ocean expansion — creates higher storm surges. Warmer air allows hurricanes to hold more water, producing more rain. Warmer oceans cause hurricanes to have faster wind speeds and stronger central pressure, making the storms more intense.
On top of these patterns, slower and stronger hurricanes make it more difficult for emergency management officials and residents to prepare for, and respond to, a disaster.
In the Bahamas, rescue crews struggled to get into the most affected areas while the storm lingered. Even after the storm began to move on, flooded roads and airport runways blocked needed aid from being delivered. On Wednesday, operations were finally able to ramp into high gear.
As the storm moved toward the U.S., aerial photos began to reveal the full scale of the devastation with large swaths of the islands flattened by Dorian’s heavy winds and rain.
“If it’s going to sit on top of you, you can’t really plan for all of the complexities and destruction that will come from something like that. The question is, how do you mitigate it?” said Wes Maul, the former director of Florida’s Division of Emergency Management who opened a natural disaster preparedness consulting firm called Admiral Strategy Group.
Stricter building codes, updated flood maps, ensuring more residents have flood insurance, improved forecasting and increased public awareness can all help reduce damage and give people a better understanding of when they need to evacuate.
“So much of this is about having a better sense that no one has zero risk,” said Kristiane Huber, a fellow at the Center for Climate and Energy Solutions. That is, even people who live further inland could be subject to severe flooding as hurricanes become more likely to stall.
As governments and nonprofits cope with the aftermath of Dorian, and the increased damage of similar hurricanes in the near future, experts warn that they need to be creating plans for decades into the future, when climate change is expected to make storms even more intense and unpredictable than they are today.