New NOAA Annual and Monthly Outlooks Help Users Plan for High Tide Flooding Risks

Business closures. Overflowing storm drains. Longer commutes. These are some of the short-term impacts coastal communities experience due to high tide flooding, defined as the overflow or excess accumulation of water that covers typically dry coastal land and occurs during high tides. It is already disruptive for low-lying areas, but as global sea levels continue to increase, so do the occurrences and severity of high tide flooding. High tide flooding is exacerbated by coinciding meteorological drivers like storms and onshore winds. NOAA’s National Ocean Service (NOS) has translated recent scientific advancements into a suite of high tide flooding products to help communities mitigate and adapt to climate change on multiple timescales.

NOAA Annual Outlooks support inter-annual planning by providing projected high tide flood frequencies at 98 long-term NOS water level stations for the next meteorological year, May to April. Predictions are derived from a statistical model incorporating historical annual high tide flooding observations with the Oceanic Niño Index. Civil engineers, city planners and emergency managers can incorporate flood frequency data into their critical infrastructure evaluations and budgeting. On the subseasonal to annual timescale, new NOAA Monthly Outlooks illustrate when and where high tide flooding is likely to occur at 67 long-term NOS water level gauges up to a year in advance. Daily likelihoods of exceeding the minor flood threshold are derived from a probabilistic model that incorporates tide predictions, sea level rise trends, and climatological non-tidal residuals as measured at NOS water level gauges. The Monthly Outlook helps local planners allocate response staff and resources when areas have the highest flood risk and provides meteorologists with an additional layer of data for making accurate flood forecasts. To give users better situational awareness, high tide flooding outlook information is also integrated into NOAA’s Coastal Inundation Dashboard, showing real-time water level conditions at over 200 NOS coastal water level stations. From the subseasonal to annual time scales, NOAA’s high tide flooding products provide stakeholders with actionable data that bolster coastal resilience.