Forecasting storm surge and coastal flooding along the Maine and New Hampshire coastline requires consideration of complex issues. The bathymetry and the irregular configuration of the northern New England coast allows for a large range of atmospheric and tidal conditions through localized channeling effects of wind and water. Access to lengthy records of real-time tide data is limited to a single point in Portland Harbor, which is problematic when forecasting over a large, data-sparse coastline. Storm surge guidance is readily available, but can have large predictive and temporal errors. These challenges exist while the population continues to increase near vulnerable beaches. Storms pose a risk to billions of dollars in personal property damage and significantly impact the marine community.
Traditionally, forecasters base flood warning decisions for long stretches of coastline on the 12 foot flood benchmark at the Portland Harbor tide gage. However, in an effort to better understand and predict a wide range of tide levels associated with coastal flooding, a coastal flood database was created (1914-2007) for Maine and New Hampshire using Storm Data Publication (http://www.ncdc.noaa.gov). This coastal flood catalogue was compared to tide archives for Portland Harbor (http://tidesandcurrents.noaa.gov). A coastal flood climatology was then created using the predicted versus observed tide levels. Storm tracks were then examined (http://www.hpc.ncep.noaa.gov/dwm/dwm.shtm) to identify predominant wind flow during coastal flood events.
The coastal flood climatology will be presented. The climatology suggests coastal flooding occurs over a wide variety of tide heights in Portland Harbor, as large ocean waves or freshwater flooding occasionally offset modest tidal surges. They are predominantly cold season events with a prevailing northeast wind. The peak observed storm tide usually occurs several minutes prior to the predicted astronomical high tide. Unusual and extreme cases will be shown, such as the October 1996, October 1998 and May 2006 coastal flood events which were coincident with extreme freshwater flooding. Finally, plans for future research will be discussed. This includes efforts to run a storm surge model to create beach specific coastal flood predictions by combining storm surge and wave guidance.