Hurricane Awareness Week observed May 16 – 22
"The greatest potential for loss of life related to a hurricane is from the
storm surge." - Brian Jarvinen, National Hurricane Center
Tuesday, May 18, 2004
MIAMI, USA: This week is Hurricane Awareness
Week and, in conjunction with GIS Caribbean and the National Hurricane Center
in Miami, we will be passing on valuable information about hurricanes and
tropical storms. Today’s topic: Storm Surge.
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. Because much of the United States' densely populated Atlantic and Gulf
Coast coastlines lie less than 10 feet above mean sea level, the danger from
storm tides is tremendous. The level of surge
in a particular area is also determined by the slope of the continental shelf.
A shallow slope off the coast (right, top picture) will allow a greater surge
to inundate coastal communities. Communities with a steeper continental shelf
(right, 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.
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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.
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. |
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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.
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