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When Hurricane Florence hit the East Coast of the United States at 7:15 ET this morning he jumped a squat near Wilmington, North Carolina. The hurricane – now downgraded to a tropical storm – hovers over the area, causing torrential rains and heading west to a glacier at three kilometers an hour, according to the National Hurricane Center. This means that the rain will continue to hit the same soggy soil, which, combined with a storm surge, leads to deadly floods. Up to now, at least two people have died, according to Vox.
"Look at how slow this system is," said NHC director Ken Graham in a Facebook briefing on Friday morning. (When Graham talks about the speed of the storm, he talks about the pace at which he moves, not the speed of the wind.) "Before everything is said and done, it will leave a trail of water and floods. impacts. "
We saw a similar pace with Hurricane Harvey, who dumped more than five feet of water in southeastern Texas, killing 68 people and causing so much damage that it was more expensive than Katrina. The slowness of Florence therefore means more danger for people on the way to the storm, as reported Kendra Pierre-Louis to The New York Times and Brian Resnick for Vox.
"Everything that comes with a hurricane lasts longer," says James Kossin, an atmospheric scientist at the National Oceanic and Atmospheric Administration. This means that the salt water is flooded by storm surges, the fresh water is flooded by rain, the damage caused by the wind. "Coming out of the door, it's not good." Kossin's research, published in June in the journal Nature, suggests that hurricanes have slowed over the past 70 years. Why? "That's the million dollar question," says Kossin.
In the case of Florence, a high-pressure system squatted in the north of Florence – which prevented Florence from going up along the coast and towards the west. This system of high pressure also aggravates the stall of the storm. "Florence is caught between the winds that want to blow towards the east and that block of high pressure that prevents it from being projected in that direction," says Charles Greene, professor of earth sciences and from the atmosphere to Cornell University. "It's a bit stuck."
The scientists The edge The interlocutors were generally reluctant to connect the dots between the slow progress of Florence in the Carolinas and global warming. The increase in global temperatures could be an explanation, but this particular connection with climate change is more controversial than the links with other hurricane features.
"With regard to hurricanes and global warming, the conclusion is very strong: they become more intense," says Dim Coumou, who heads the research group Atmospheric Circulation and Extreme Conditions at the Research Institute on the climatic impacts of Potsdam. The warmer air can also hold more water vapor, which can result in more torrential rains, he says. But when it comes to a hurricane's pace as it moves from place to place, Coumou says, "There is more uncertainty here."
In general, we know that, with global warming, the temperatures at the poles rise more than at lower latitudes. And as the difference in temperature between the Arctic and the equator decreases, the pressure gradient that drives large-scale air currents, such as the jet stream, also decreases. According to Kossin, this could result in a slowdown in the circulation of weather systems, including hurricanes such as Florence.
Other climate scientists are taking similar models. Michael Mann, Professor of Atmospheric Science at Penn State University, linked this amplified warming of the Arctic to jet-related behaviors "associated with slowing weather systems, including what we saw with hurricanes during the last decade as Harvey, Irene. , and now Florence, "said Mann The edge in an email. The study, co-written with Coumou, was published in the journal Scientific reports in 2017.
Scientists are still determining the link – if there is a link – between the time of a hurricane and climate change. On one side, says Kossin, this could be a natural variability. On the other hand, he says, if there is "a human footprint related to this warming, we expect that the slowdown will continue – at least the part caused by human activity," says -he. But there is certainly something happening. "It's worrying that we're seeing more hurricanes and slower traffic," says Coumou. "It must be understood."
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