The Southeastern United States is reeling from Hurricane Helene, a monstrous storm that made landfall in Florida on Thursday before cutting a terrifying path all the way up to Tennessee. How did it get this bad?
The storm has killed more than 100 people, and hundreds more are still missing. Power is out for millions of people. Residents around Asheville, North Carolina — one of the hardest-hit areas — are reportedly struggling to find food, water, and cellphone service. We don’t yet know what the full impact of the storm is; search and rescue missions are still underway, and scientists are finalizing data on how powerful the storm was.
But it’s clear that the storm was disastrous because of its unusual size, intensity, and speed. The perfect conditions were in place to supercharge the storm.
“It had all the different weapons at its disposal that a hurricane [can have],” says John Knox, distinguished teaching professor and undergraduate coordinator of the Atmospheric Sciences Program at the University of Georgia. “Everything that we say a hurricane can do, Helene did do.”
While Helene was still churning in the Gulf of Mexico, forecasters were already warning that the storm was going to be “unusually large.” At its maximum, tropical storm-force winds extended nearly 350 miles away from Helene’s center. That enormous reach put Helene in the 90th percentile for storm size, according to the National Hurricane Center. On the ground, that means the effects of the storm — wind, storm surge, and heavy rainfall — were felt across an unusually large area.
Not only was the storm huge but it was also stronger than most. Storm systems this large don’t always develop a small inner core that allows them to quickly strengthen. But Helene was able to form a relatively small eye and then rapidly intensify, a term used to describe tropical storms with sustained wind speeds that rise by at least 30 knots (roughly 35 miles per hour) in a 24-hour period.
It made landfall with winds reaching 140 miles per hour, making it a major storm and a Category 4 out of 5 on the Saffir-Simpson hurricane scale.
Helene packed a punch with water, too. When it hit Florida’s Big Bend region, it brought a massive storm surge, inundating the coastline with up to 15 feet of seawater. The underwater topography off Florida’s west coast, with a more gradual incline, acted like a ramp, making it easier for the storm to bring a taller wall of water with it. The sheer size of the hurricane also meant that the storm surge flooded a wider area.
Heavy rainfall dropped more water onto communities, leading to historic flooding in western North Carolina. Close to 14 inches of rain were recorded at the Asheville airport over three days between September 25th and 27th. The highest preliminary total was more than 31 inches of rain, recorded in Busick, North Carolina.
“It certainly has been a very catastrophic event in portions of Southeast US, especially the southern Appalachians where they’ve seen just tremendous amounts of rainfall and flooding,” says Daniel Brown, branch chief of the hurricane specialist unit at the National Hurricane Center. But with damage and fatality reports still coming in, it’s probably still too soon to know how Helene compares to other storms, he says.
Source: https://www.theverge.com/2024/9/30/24258295/hurricane-helene-monster-storm-speed-strength-size