An Evolving NOAA Operational Paradigm for Extratropical Storm Surge and Coastal Inundation

The historic discontinuity in how NOAA’s National Weather Service (NWS) forecasts coastal inundation and storm surge impacts during a tropical cyclone and during non-tropical events (e.g. Nor’easters) has long been identified as a concern by its partners and users. These discontinuities were especially noteworthy during Hurricane Sandy in 2012. NWS currently uses different forecast products depending on whether the storm is tropical or non-tropical in nature. In turn, these products feature fundamental differences in language, thresholds, geographic range of forecasts (zone-based vs. grid-based warnings), colors, and how the information is disseminated. These differences can lead to confusion and misunderstanding of risk, particularly in areas that regularly experience both tropical and non-tropical storm surge events, such as along the U.S. East Coast. NWS, in partnership with NOAA’s National Ocean Service (NOS) is committed to closing the gap in forecasting methodology between tropical and non-tropical storm surge events.

Over the last few years, progress has been made on increasing consistency in communication around coastal inundation. Immediately following Sandy, policies were updated to provide continuity in forecasting for storms transitioning from tropical to extratropical. More recently, steps have been taken to ensure consistent referencing of both coastal water level forecasts and observations, using ground level as a base elevation. Work also continues towards ensuring the warned area most closely matches the area at risk, regardless of whether coastal flooding is attributable to a tropical cyclone or non-tropical event. Additionally, NOAA continues to work toward the goal of providing total water forecasts, and seamlessly coupling freshwater hydrologic models with coastal hydrodynamic and storm surge models, to provide a more complete picture of flood risk.

This presentation will provide an update on recent development of a concept of operations for non-tropical storm surge forecasts by NWS and outline near and long-term actions planned to implement this new operational paradigm.