Recent Developments in NOAA’s Subseasonal to Annual High Tide Flooding Outlooks

Coastal flooding is becoming more frequent and severe across the U.S. due to sea level rise, resulting in increased risk of infrastructure damage, natural resource degradation, and threats to public safety. Advance notice of flooding events can significantly aid in the preparation and planning to minimize these risks and increase resilience of our coastal regions. Although major flooding events, such as from hurricanes and nor’easters, get much of the attention, they are difficult to predict at timescales greater than a week or two. Though lesser in magnitude, routine flooding, often termed High Tide Flooding (HTF), can also cause significant impacts and disruptions to communities. At timescales of approximately two weeks or more, likelihoods of HTF events are often associated with aspects of the overall climate system, such as mean sea level trends, astronomical tides, seasonal variability, and climate modes (e.g., ENSO) of the atmosphere and ocean.

NOAA Center for Operational Oceanographic Products and Services (CO-OPS) utilizes these climate inputs to provide outlooks of HTF at individual tide gauges across subseasonal to seasonal (S2S) and seasonal to annual (S2A) timescales. Research has been ongoing to improve HTF outlooks in two primary ways: 1) better understanding of the drivers and impact thresholds of coastal flooding in different parts of the US, and 2) modifications to the existing HTF modeling framework, such as incorporating S2S sea surface height modeling, improved statistical distributions and methods, and evaluating dependence upon trends and tidal predictions. Additionally, NOAA has recently developed the Coastal Ocean ReAnalysis (CORA) dataset, which assimilates tide gauge observations with coupled ADCIRC + SWAN hydrodynamic modeling to generate hourly water levels along the Atlantic and Gulf coasts from 1979 to 2022. CORA data can produce annual and monthly climatologies of HTF frequency and depth at locations “between the gauges,” to enhance the spatial coverage of CO-OPS HTF products and support flood resilience planning in communities that are currently not being monitored. This presentation will highlight the latest developments and ongoing research in NOAA’s S2S and S2A HTF efforts.