A coastal flood occurs when low lying land areas bordering a large body of water are inundated. Coastal flooding may be caused by abnormal rise in water level associated with an approaching ocean storm or by large breaking waves on the shore from large ocean swells. The extent of coastal flooding depends upon the tide levels, the underwater and shoreline topography and the runoff from rivers and estuaries.
Coastal floods are often associated with high water from a storm surge, caused by winds generated by tropical (hurricanes) or extratropical cyclones. Coastal flooding can be produced also by a tsunami, a seismic sea wave produced by earthquakes, landslides or volcanic activity; these waves are erroneously called tidal waves. Alaska, Hawaii and the Pacific coast are most vulnerable to a tsunami.
The greatest danger and damage associated with most tropical cyclones (hurricanes) is the storm surge. A storm surge is a dome of water, perhaps 50 miles wide that sweeps across the coastline ahead of a tropical cyclone landfall. The magnitude of a storm surge depends upon the strength of the storm, the ocean bottom conditions where the surge comes onshore, the storm's movement relative to the shoreline, and the tides at landfall time.
In addition, the destruction of the storm surge is often compounded by the hammering effect of the breaking waves. Because many tropical cyclones produce excessive rainfall rates and total amounts of precipitation even after landfall, they may be also responsible for floods and flash floods. The strong and gusty winds, coupled with the possibility of tornadoes, are added perils to residents of areas near the landfall of a hurricane.
Coastal floods and beach erosion can also be associated with extratropical cyclones, such as the "nor'easters", that may batter the East Coast from Cape Hatteras to Maine, especially during the winter season. Coastal flood watches and warnings are issued by certain designated National Weather Service Offices and pertain to the region extending from the ocean beaches inland, including waterways, estuaries and river mouths.
The National Weather Service issues various public statements for tropical weather systems as well as for other types of situations that can cause coastal floods. These statements follow the advisory, watch and warning format previously described, and they are intended to inform the coastal residents and commercial and recreational marine interests of a potentially hazardous weather situation. A full description of these statements appears in the Tuesday optional Supplemental Summary Information .
To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications', Week 12 Chapter Progress Response Form, under section B. Daily Summary.