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A Next-Generation Coastal Ocean Operational System: Probabilistic Flood Forecasting at Street Scale

Recent hurricanes have demonstrated the need for real-time flood forecasting at street scale in coastal urban areas. Here, we describe the high-impact high-resolution (HIHR) system that operationally forecasts flooding at very high resolution in the New York–New Jersey metropolitan region. HIHR is the latest upgrade of the Stevens Flood Advisory System (SFAS), a highly detailed operational coastal ocean modeling system. SFAS, based on the Hydrologic–Hydraulic–Hydrodynamic Ensemble (H3E) modeling framework, consists of four sets of nested coastal and inland flood models that provide ensemble flood forecasts with a horizon of at least 96 h from regional to street scales based on forcing from 100 different meteorological output fields. HIHR includes nine model domains with horizontal resolution ranging from 3 to 10 m around critical infrastructure sites in the region. HIHR models are based on an advanced hydrodynamic code [the Stevens Estuarine and Coastal Ocean Model (sECOM), a derivative of the Princeton Ocean Model] and nested into the H3E models. HIHR was retrospectively evaluated by forecasting the coastal flooding caused by Superstorm Sandy in 2012 using water-level sensors, high-water marks, and flood maps. The forecasts for the 95th percentile show a good agreement with these observations even three days before the peak flood, while the 50th percentile is negatively biased because of the lack of resolution on the meteorological forcing. Forecasts became more accurate and less uncertain as the forecasts were issued closer to the peak flooding.