Impact of Hurricane Florence (2018): Extreme Flooding from a Combination of Storm Surge, Heavy Rainfall, and River Outflow

A rare combination of storm surge, heavy rainfall and river overflow produced a widespread, coastal and inland flooding during the landfall of Hurricane Florence (2018), causing $17 billion in damage and 30 direct casualties from South Carolina to Virginia. The broad range of spatial and temporal scales and complex physical processes associated with storm surge, rainfall, and river overflow created a "perfect storm" for a extreme flooding event induced by Hurricane Florence. During landfall, Florence followed an unusual south-westward track and its translation speed decreased dramatically. As a result, heavy rainfall from slow-moving rainbands combined with storm surge to produce localized inundations and flash floods along the coastal region. In the following days, orographically-enhanced precipitation across the Appalachian Mountains’ foothills contributed to major river flooding in the interior region. Such a complex combination made impact forecasting and risk communication particularly challenging. The hurricane impact forecasting and communication had a major challenge in part due to the lack of operational forecasting models that are capable of representing the complex coupled atmosphere-wave-ocean-land processes. The objective of this study is to better understand and predict the processes involved in Florence’s impact using the Unified Wave Interface Coupled Model (UWIN-CM), a fully-coupled atmosphere-wave-ocean model. We will address the role of the storm-induced large ocean surface waves, heavy rain, and storm surge to coastal flooding, and implication for river overflow over inland regions. We are examing the importance of topography in enhancing precipitation and river flooding in areas far away from the storm center. We will discuss the potential improvement of communicating hurricane hazards by the new generation of fully coupled models that can produce explicit, informative quantitative flooding forecasts during tropical cyclones landfall events.