Catastrophic flash flooding from these bands ensued throughout the day, washing out roads and prompting water rescues. Although the center of Florence progressed inland over South Carolina, offshore convective available potential energy values of 1,000–2,000 J/kg and strong mid-level winds continued fueling the aforementioned rainbands. A low-risk of tornadoes accompanied the heavy rain across North Carolina. Minimal diabatic heating stemming from the hurricane's lack of a thermal gradient kept the threat of tornadic storms low, with the primary driving force being ample atmospheric moisture. Small-scale training supercells—series of severe storms that continuously develop, track across, and dissipate over the same areas—developed between Morehead City and Wilmington during the overnight hours of September 14–15. Record flooding ensued along the Cape Fear, Northeast Cape Fear, Lumber, and Waccamaw rivers; nine USGS river gauges observed all-time crests. Flooding persisted along multiple rivers for more than a week after the storm. Approximately 86,000 homes across North and South Carolina were flooded or otherwise damaged. Total damage between the two states reached an estimated $24 billion, ranking Florence as the ninth-costliest hurricane in United States' history. Florence weakened below hurricane strength by 00:00 UTC on September 15. Its close proximity to the coastline enabled it to maintain its organization and only slowly degrade. Throughout the majority of the day intense rainbands persisted over southern North Carolina, with six-hourly accumulations averaging in two bands extending from Brunswick to Bladen counties and Pender to Sampson counties. Aided by an anticyclone, this band stretched across 350 mi (565 km) along the eastern side of Florence. The heaviest rains shifted to South Carolina early on September 16; estimated rainfall rates reached per hour in Dillon, Marion, and Marlboro counties. The system finally weakened to a tropical depression over South Carolina by 18:00 UTC on September 16, more than two days after it made landfall. Florence accelerated north along the western edge of the ridge previously steering it west. It eventually became extratropical over West Virginia on September 17. Heavy rains propagated north along with the circulation center; however, rainbands extended from Virginia to South Carolina through September 17 with a narrow band of convection pivoting along the eastern slopes of the Appalachian Mountains. An approaching frontal system caused the remnant system to accelerate east, and ultimately resulted in its dissipation over Massachusetts on September 18.