A storm surge results from an atmospheric low-pressure system and strong winds blowing onshore during large storms. Strong low-pressure systems raise the surface of the ocean due to their reduced atmospheric pressure. Winds that blow onshore cause water to flow toward the coastline, resulting in wind set-up (rise in water level from wind stresses on the surface of the water). As waves enter shallow coastal water and break, wave set-up (rise in water level due to breaking waves) further raises the water level. Waves rushing up a beach or structure generate additional wave run-up. All of these factors contribute to high water levels that are superimposed on the predicted tide. MSL datum = mean sea-level datum.
Adapted from Mullan et al., 2005.