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| Hurricanes, El-Niño, & Northeasters - An Introduction |
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| Extreme Storm Impact Studies: |
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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
El-Niño
Northeasters
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
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Coastal erosion: Cliff erosion near Pacifica, CA
in February 1998, following a series of severe storm events.
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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
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Dune erosion:
Compared pre- and post-storm beach profiles show dune erosion
at Assateague Island (MD, VA) caused by a severe northeaster.
Note the exaggeration of the vertical scale to emphasize the changes.
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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.
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U. S. Department of the Interior | U.S. Geological Survey