by the position of the subtropical high. Hurricanes have a definite seasonality. Even
though it can be said that it is “always summer” in the tropics, different portions of
the year have different flow regimes. The months just after the summer solstice of
the respective hemispheres are the times of hurricanes. For instance, the North
Atlantic hurricane season is defined as June 1 through November 30. In this region,
hurricanes are most common at the beginning of September. The temporal occur-
rence of hurricanes is closely related to the extent of the warm sea surface temper-
atures needed to cause and maintain them.
Around the world, hurricanes are named through the auspices of the World
Meteorological Organization, which keeps six-year rotating alphabetical lists of
upcoming names for each ocean basin. There is an alternation between men’s
and women’s names appropriate to countries surrounding the ocean basin; the let-
ters Q, U, X, Y, and Z are not used. Storms notable for damage or loss of life can
be permanently retired and other names substituted. Physical damage from hurri-
canes can result from one of several causes. The most utterly destructive in terms
of property and life is the storm surge. The storm surge is a large lens of water
pushing onshore and does not refer to the wind-generated waves of a hurricane.
Sea level is a vertical function of atmosphere pressure. Near the center of the
storm, water is piled up by the combination of dramatically low surface pressure
and high winds. Storm surges have been known to top 8 m with individual events
being governed by the structure of the individual storm and the shallowness of the
Hurricanes 179Barrier Islands
Paralleling many of the world’s coastlines are long, narrow stretches of sandbars called
barrier islands. These can range from a few hundred meters to many kilometers from a coast
and can be well over 100 km long. Average elevations on barrier islands are usually a couple of
meters. They are present on the shallow portions of continental shelves and most result from
plentiful sand deposited by breaking waves. Coastward from barrier islands there are areas of
shallow, protected saltwater known as lagoons. Protected from the greatest motions of the
oceans, lagoons produce fertile and biodiverse ecosystems and are key to the life cycles in
some oceanic fish. Prominent barrier islands in the United States include Padre Island of
Texas and the Outer Banks of North Carolina. Elsewhere, Colombia, the Netherlands, and
India are among countries with extensive barrier island systems. It is apparent that many
barrier islands have had a complicated history as sea level fell dramatically during the Pleisto-
cene and then rose during recent times. Barrier islands tend to be only a few thousand years
old and are capable of migration and disappearance as sea levels rise and/or sand supplies
lessen. Large storms, particularly hurricanes, are capable of breaching barrier islands to make
inlets to the lagoons. Humans have built resorts and cities (e.g., Miami Beach) on barrier
islands, thus presenting an inherent locational danger.