Forecasts of coastal flooding, splash-over and beach erosion historically have not been depicted together. Unfortunately, environmental conditions which create these phenomena are complex and cross several disciplines, yet systematically influence each other. As a result, operational meteorologists are challenged to make subjective forecast decisions based on numerous sets of multi-scale parameters.

The synergistic effects of extreme tides and large battering waves often lead to splash-over and coastal flooding. Splash-over can be described as damage driven by large waves “over-topping” obstacles resulting in significant beach erosion, whereas coastal flooding is the “inundation of land areas adjacent to bodies of salt water”. Splash-over events are more frequent than coastal inundation and can cause significant damage.

Recently, there have been efforts to improve the visualization of water levels over large geographical areas. In particular, the Advance Circulation (ADCIRC) model employs 10 m wind guidance from the Weather Research and Forecast (WRF) model to produce hourly water level forecasts along the East coast of the United States and the Gulf of Mexico. However, this model does not explicitly calculate localized sea level rises and beach erosion produced by wave action. In an effort to incorporate this dynamic, the ADIRC model was graphically combined with the Wave Watch III model to produce hourly plots of water level in Portland Harbor versus near-shore wave heights. The result is a web-based, experimental “Coastal Flood Nomogram”. The product is available on the Gulf of Maine Ocean Observing System (GoMOOS) website at www.gomoos.org.

The visualization focuses on the combined dynamical forces of storm tides and large battering waves by simultaneously plotting this information on one diagram. Coastal flooding and splash-over benchmarks were then appended to the nomogram. These thresholds were based on empirically derived relationships of water level and waves that correlated with damage found in the Northern New England climatology. When the plot is animated, users from a wide variety of audiences can assess the threat of potential coastal hazards.

A review of the coastal flood climatology will be shown to provide the basis of benchmarks established for the coastal flood nomogram. Nomogram animations will then be demonstrated, focusing on the 16 April, 2007 (Patriot's Day storm). Future improvements will be discussed which will allow interactive adjustments of predicted water level and wave heights by emergency managers.