Flash Flood in Buncombe County, North Carolina

Historic and catastrophic flash flooding developed along the Swannanoa River basin during the early morning hours as rainfall rates began to intensify as tropical rainbands near the center of Helene swept across the area. Numerous structures and roads were inundated in the city of Black Mountain, the Swannanoa community and surrounding areas, with multiple homes and businesses and numerous roads destroyed. The most devastating flooding occurred in the Asheville area, as numerous businesses were damaged and some completely destroyed or swept away in Biltmore Village. The stream gauge on the Swannanoa River at Biltmore Village crested at just over 26 feet, which was more than 5 feet higher than the crest during the Great Flood of 1916. Multiple landslides occurred throughout the Swannanoa Valley, with some of those damaging or destroying homes. Fourteen people died throughout the basin, mainly along the Swannanoa River. Almost all of these fatalities occurred in structures that were swept away in floodwaters, although at least one was attributed to a landslide. Three-day rainfall amounts ranged from 9-15 inches across much of the county to 15-22 inches with locally higher amounts across the far eastern part of the county, including in the Swannanoa headwaters.

Tropical Cyclone Helene began organizing over the western Caribbean on the 23rd and 24th of September before rapidly intensifying as it moved north through the eastern Gulf of Mexico on the 25th and 26th. A plume of moisture extending from the intensifying storm interacted with a slow-moving cold front to produce a band of widespread heavy rain showers and embedded scattered thunderstorms over the southern Appalachians and vicinity on the 25th and 26th, resulting in a predecessor heavy rainfall and flash flooding event over these areas. Helene made landfall in the Florida Big Bend and moved quickly N/NE through Georgia before turning toward the N/NW once the remnant center reached northeast Georgia. Tropical rainbands around the center of Helene swept over areas with already-saturated soils over the mountains and foothills during the early morning of the 27th, resulting in extreme rainfall and record, catastrophic flash flooding across multiple basins with headwaters near the Blue Ridge escarpment. Due to its quick movement, Helene was still a strong tropical storm when the wind field reached the western Carolinas and northeast Georgia. Frequent wind gusts of 55 to 70 mph, with occasional gusts of 80 mph...and likely as high as 100 mph across the higher elevations combined with saturated soils to produce widespread damage to trees and electrical infrastructure. Across the mountains, some east and southeast-facing slopes above 3000 feet saw canopy-loss of 80% or more. Hundreds of trees fell on houses, vehicles, and power lines throughout the area, resulting in several fatalities. Almost all customers in several counties lost power for at least a brief period. Most people were without power for at least a couple of days, while thousands were without power for a week or more.