At present, USGS investigates three types of severe coastal storm impacts: hurricane impacts on the southeast U.S., extra-tropical storm impacts on the U.S. west coast during El-Niño winters, and 'northeaster' impacts on the U.S. east coast.

HURRICANES

Hurricanes are tropical storms that have a sustained wind speed greater than 75MPH. In the northern hemisphere, these low pressure systems rotate counterclockwise. As a hurricane approaches the coast, the wind speed on the right side of the storm is added to the forward speed of the storm. Hence, the greatest impacts from storm surge, wave battering and wind speed tend to occur to the right of the eye at landfall. Storm surge is an increase in sea level along the coast caused primarily by strong onshore winds and low barometric pressure. The strongest hurricanes are Category 5, having sustained wind speeds in excess of 155MPH and storm surge in excess of 6 m (20 ft). In recorded history, only two Category 5 hurricanes have made landfall in the United States.

EL-NIÑO

During severe El-Niño, the jet stream over the Pacific Ocean tends to be more southerly than normal, guiding winter extra-tropical storms into California and bringing extensive rainfall and large waves to the California coast. During the severe El-Niño's of 1982-83 and 1997-98 extensive coastal erosion and damage occurred along the west coast. Under El-Niño conditions of equatorial warming in the Pacific, hurricanes are less frequent in the north Atlantic. The reoccurrence of La-Niña, equatorial cooling in the Pacific, coincides with active hurricane seasons for the southeast United States.

NORTHEASTERS

Northeasters, or winter extra-tropical storms impacting the east coast of the United States, can cause considerable coastal change and damage. For example, one of the most destructive storms to ever impact the mid-Atlantic states was the Ash Wednesday storm of 1962. Extensive coastal change occurred over 1,000 km of coast. Northeasters owe their destructive power to their long duration. Winds are typically below hurricane force, but can persist for several days to a week generating large waves and enhanced storm surge. In comparison, hurricanes are more severe in terms of wind speed and storm surge but the shoreline impacts tend to be more localized, confined to order 100 km of coast. Hurricanes also tend to be more short-lived moving across coastal areas in hours rather than days.