Flooding in North Carolina after Helene: Heavy rain caused chaos

Meteorologists had warned that Hurricane Helene would become a “once in a generation” storm for parts of the Appalachian Mountains, and the forecast proved tragic in mountainous parts of western North Carolina, eastern Tennessee, South Carolina and Georgia applicable.

Now dozens of people are dead. Hundreds are missing. Homes and lives were destroyed. Roads destroyed. Damages in the double-digit billion range.

The copious amounts of rain that fell across the region’s unique terrain before and during Helene resulted in “the most severe flooding ever observed” in western North Carolina, Corey Davis, North Carolina state deputy climatologist, said Monday in a blog post.

Graphic: How flood damage is cutting communities in North Carolina off from emergency relief

The catastrophic flooding disaster was caused by an unfortunate combination of weather, hydrology and geography, experts told USA TODAY on Monday.

Almost unimaginable amounts of rain fell along a 200-mile swath of the United States, pouring down from high peaks and turning raging mountain streams into unrecognizable torrents. Torrential waters flooded valleys, completely surrounded a hospital in East Tennessee and cut off entire communities in western North Carolina.

Rain before the storm

Rainfall from Helene would have been enough to trigger flooding anywhere, but it was exacerbated by a weather front that stalled over the Appalachian Mountains before then-Tropical Storm Helene arrived, said David Easterling, a rainfall expert at the National Centers for the National Oceanic and Atmospheric Administration Environmental Information in Asheville, North Carolina.

In fact, on Wednesday, September 25, at 5 p.m., a thousand miles from Asheville, Hurricane Helene reached Category 1 storm strength with its center north of Cancun, Mexico – still more than 500 miles and 30 hours from its final landfall the Florida coast, Davis said.

But by then it was already raining in the mountains as a line of slow showers had formed from Atlanta across the southern Appalachians along a stalled cold front fed by tropical moisture from the edges of Helene’ to the south.

The arrangement between the front and Helene’s enormous circulation was able to send a veritable hose of water from the warm Gulf of Mexico into the mountains before the storm arrived. Then the storm, enriched with water it had picked up on its journey through the Gulf, brought additional rain.

Rainfall amounts ranging from 6 inches to 30 inches or more fell over three days in a region from northern Georgia through western North Carolina, eastern Tennessee to Virginia.

Mountains increased the rain

The mountains themselves added to the rainfall in some places because they contribute to the upwelling that leads to more rain during thunderstorms, Easterling said.

“It rained for at least 30 hours,” he said. And in some places it was more than 25 inches.

“All the rain falls down and gets channeled into smaller streams to flow into larger streams,” he said. And those streams carried their water toward the larger rivers, he said.

Unfriendly terrain

Not only did the terrain increase rainfall, it also caused colossal flooding.

“The terrain there — steep slopes and flat ground — is not conducive to heavy rainfall,” Russ Barton of NOAA’s National Water Center told USA TODAY. He said most of the infrastructure is in the valleys, where all the water flows during a flood.

All the water flowed into these larger rivers, flooding anything near a river, said Easterling, who lives in the area and is among the thousands without power.

He said strong winds toppled trees and destroyed power lines, as well as mudslides and landslides that caused poles to collapse throughout the area, he said.

“It’s just a mudslide and you might end up with 5 to 10 feet of mud left. It cut off I-40 and that can destroy a whole house,” he said. “There is no telling how many lives were lost.”

How much water was it?

Near Lake Lure, North Carolina, where famous scenes from the movie “Dirty Dancing” were filmed, the current in Cove Creek surged between Tuesday and Thursday, carrying 32 times more water, according to the U.S. Geological Survey. The area around Lake Lure and Chimney Rock suffered catastrophic damage.

At a water monitoring station on the French Broad River in Asheville, a gauge measured 12 inches of rain from Wednesday through Friday, according to USGS data. But the river also collects water from a network of streams and streams to the north, where rain fell in even larger quantities.

The flow in the river increased twenty-fold between Tuesday and Thursday. As the height and volume increased, the water became increasingly cloudy and full of mud and debris. According to USGS data, the gauge reported zero on Friday and Saturday, but then started again on Sunday after water levels began to fall.

At that point, the swollen French Broad was flowing at a rate of more than 240,000 gallons per second, enough to fill an Olympic-sized swimming pool every 2.74 seconds.

Contributors: Beth Warren, The Tennessean, USA TODAY Network.

Flooding in North Carolina after Helene: Heavy rain caused chaos

ByJasper

Rain before the storm

Mountains increased the rain

Unfriendly terrain

How much water was it?

By Jasper

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