The deadly floods in Helene show that the hurricane threat is shifting far inland

(Bloomberg) — Hurricane Helene has killed more than 100 people in six southern U.S. states — and most of the victims lived hundreds of miles from where the storm made landfall.

After hitting Florida’s west coast last week, Helene triggered catastrophic flooding in the Appalachian Mountains. Its devastation was due primarily to two factors: its enormous size and the significant amount of moisture it absorbed over open water.

Oppressive ocean temperatures caused by climate change are causing storms to suck in more water vapor and trigger torrential rains. And while researchers don’t attribute the hurricane’s size to global warming, Helene’s width does – with winds that stretched more than 310 miles (499 kilometers) at landfall, it was larger than 90% of the region’s hurricanes over the past two decades – this has meant flooding cities and towns far from the coast.

“Helene was, to put it bluntly, sort of the worst of them all,” said John Cangialosi, senior hurricane specialist at the U.S. National Hurricane Center in Miami. “It’s one of those hurricanes with all the dangers. You will hear that some storms are wind machines, others produce storm surges, and others bring rain. Helene caused all these dangers – significantly.”

Helene’s Chaos shows how a hotter planet means more people are at risk during extreme weather events, challenging assumptions about preparedness for storms and other natural disasters. Residents along parts of Florida’s west coast faced evacuation orders as Helene approached, but people to the north largely did not receive similar warnings until levee breaches became imminent.

Helene emerged from the Central American Gyre, a widespread low-pressure area over the western Caribbean that tends to produce storms this time of year, said Phil Klotzbach, a hurricane researcher at Colorado State University. Any storm generated by a circulation area like the Central American Gyre – as opposed to a smaller low pressure band – tends to inflate and maintain strength as it marches across the Atlantic basin toward populated areas.

“If a storm forms from a large pre-existing circulation, it will be big,” Klotzbach said. “Typically, one reason big storms are bad is that they tend to have a larger footprint of wind and precipitation.”

Helene’s wind and rain were exceptionally strong. Research has shown that warming oceans caused by climate change are triggering more severe hurricanes, defined as Category 3 or higher on the five-point Saffir-Simpson scale. It is now more likely that hurricanes will intensify quickly, their strength will explode within a short period of time and there will also be more frequent heavy rainfall.

That will pose a challenge for forecasters like Cangialosi, who already struggle to inform the public about risks. People are used to hurricanes behaving a certain way, Cangialosi said, and many tend to ignore storm size, which can determine how far inland the storm will be felt. This means that past storm experiences may not reflect current reality.

“The biggest problem we have is people living through their experiences,” Cangialosi said. “We don’t want you to necessarily just compare storms.”

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