Historic Rainfall and Record-Breaking Flooding from Hurricane Florence in the Pee Dee Watershed

Abstract

For the third time in four years, record-breaking flooding occurred in South Carolina. Hurricane Florence, which made landfall near Wrightsville Beach, North Carolina, on September 14, 2018, moved slowly across South Carolina from September 14–17, 2018. Over those four days, heavy rain fell over portions of the Pee Dee Watershed and eastern North Carolina, with over 30 inches of rain measured by an observer in Swansboro, North Carolina. Most of the excessive rainfall was confined to the Pee Dee region, with reported totals of over 24 inches in Horry County, while closer to the Savannah River Valley observers measured less than an inch of rain. Unlike the more recent flooding events across the state, not as many rainfall records were set during this event. The amount of rainfall at various locations, and at different time intervals (1-day, 2-day, 3-day, and 4-day), had a statistical probability of occurrence of 0.1%, or 1 in 1,000 chance of happening in any given year, according to the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 (Bonnin et al., 2004). The rainfall associated with Hurricane Florence produced a long duration and significant flood that impacted many of the same communities still recovering from the October 2015 floods and Hurricane Matthew in 2016. Many of the rivers and streams within the Pee Dee Watershed experienced major or extreme flooding, with six stream gauges reaching record peaks, some surpassing the records set in 2016. This report provides an overview of the antecedent conditions, a synoptic summary of the event, and documentation on the meteorological and hydrological impacts observed across the Palmetto State.