Storms
Storm surge is simply water that is pushed toward the shore
by the force of the winds swirling around the storm. This
advancing surge combines with the normal tides to create the
hurricane storm tide, which can increase the mean water level
15 feet or more. In addition, wind driven waves are superimposed
on the storm tide. This rise in water level can cause severe
flooding in coastal areas, particularly when the storm tide
coincides with the normal high tides.
The level of surge in a particular area is also determined
by the slope of the continental shelf. A shallow slope off
the coast ( top picture) will allow a greater surge to inundate
coastal communities. Communities with a steeper continental
shelf (bottom picture) will not see as much surge inundation,
although large breaking waves can still present major problems.
Storm tides, waves, and currents in confined harbors severely
damage ships, marinas, and pleasure boats.
One tool used to evaluate the threat from storm surge is the
SLOSH model. Emergency managers use
this data from SLOSH to determine which areas must be evacuated
for storm surge. The links below provide some altered photos
that show how the intensity of the storm (as given by the
Saffir-Simpson Hurricane Scale) affects the possibility of
flooding from storm surge at two locations. Storm surge also
affects rivers and inland lakes, potentially increasing the
area that must be evacuated.
In general, the more intense the storm, and the closer a
community is to the right-front quadrant, the larger the area
that must be evacuated. The problem is always the uncertainty
about how intense the storm will be when it finally makes
landfall. Emergency managers and local officials balance that
uncertainty with the human and economic risks to their community.
This is why a rule of thumb for emergency managers is to plan
for a storm one category higher than what is forecast. This
is a reasonable precaution to help minimize the loss of life
from hurricanes.
Wave and current action associated with the tide also causes
extensive damage. Water weighs approximately 1,700 pounds
per cubic yard; extended pounding by frequent waves can demolish
any structure not specifically designed to withstand such
forces.
The currents created by the tide combine with the action
of the waves to severely erode beaches and coastal highways.
Many buildings withstand hurricane force winds until their
foundations, undermined by erosion, are weakened and fail.
In estuaries and bayous, intrusions of salt water endanger
the public health and send animals, such as snakes, to flee
from flooded areas and take refuge in urban areas.
Severe weather safety tips
Planning for a Storm
Storms Supply Kit
