EM 1110-2-1100 (Part II)
(Change 1) 31 July 2003
the United States since 1876. The effects of Hurricanes Hugo in 1988 and Andrew in 1992 have shown the
tremendous potential for coastal destruction that can accompany these storm systems in southern reaches of
the Atlantic coast. The effects of the Hurricane of 1933 in New England and Hurricane Bob in 1990 show
that even farther north, the risk of hurricanes cannot be neglected.
c.
Gulf of Mexico.
(1) Table II-2-4 shows the same information for the U.S. Gulf coast as was given in Table II-2-3 for the
Atlantic coast. Mean wave heights for this coast are often considered to be considerably lower than those on
the Atlantic coast; however, as can be seen in this table, this is not evident in the wave data. In fact, mean
wave heights near Brownsville are larger than anywhere on the Atlantic coast. The reason for this is that the
mean wind direction in this location is directed toward land, whereas, along the Atlantic coast, the mean wind
direction is directed away from land except for areas south of Jacksonville, FL. Mean wave heights generally
decrease eastward to the Appalachicola area and then remain fairly constant southward to the Florida Keys.
(2) Many of the larger waves in the Gulf of Mexico are generated by storms that are centered well to
the north over land. Thus, large waves can be experienced at offshore sites even when conditions along the
coast are quite calm. Typical day-to-day wave conditions in many coastal areas are produced by a
combination of relatively small synoptic-scale winds and sea-breeze circulations. As noted in Table II-2-2
in this section, these waves are rarely very large. At times, the Gulf of Mexico comes under the influence
of large-scale high pressure systems, with winds blowing from east to west across much of the Gulf. These
winds are primarily responsible for the higher wave conditions in the western Gulf. Due to the lack of strong
storms centered within the Gulf, there is little or no swell reaching Gulf shorelines, with the notable exception
being swell from remote tropical systems. Consequently, except for the extreme western Gulf of Mexico,
mean wave periods tend to be somewhat smaller than those along the Atlantic coast (4 to 6 sec).
(3) The 90th percentile wave heights indicate that typical large wave conditions along the coast are only
about 50 percent larger than the mean wave heights (compared to about a 100-percent factor for the Atlantic
coast). This is consistent with the idea that the Gulf of Mexico is, in fact, a calmer basin than the Atlantic.
These wave heights in the Gulf vary from a maximum of 1.5 m near Brownsville to 1.2 m along Florida's
west coast. Associated wave periods range from 6 to 8 sec.
(4) Values of the 5-year wave heights in the Gulf of Mexico vary from 3.2 m along the west coast of
Florida to 4.6 m near Brownsville. Associated wave periods vary between 9 and 10.5 sec. Some of the higher
non-tropical waves in the Gulf of Mexico are generated by wind systems called "Northers." Since these
winds blow out of the north, they typically do not create problems at the coast itself, but can produce large
waves at offshore sites. Occasionally an extratropical cyclone will develop within the Gulf. One example,
the intense storm of 10-13 March, 1993 (the so-called "Storm of the Century"), produced high surges and
large waves along extensive portions of Florida's west coast. Damages and loss of life from this storm
demonstrated that, although rare, strong extratropical storms can still be a threat to some Gulf coastal areas.
(5) The primary source of extreme waves in the Gulf of Mexico is hurricanes. Hurricanes Betsy (1965),
Camille (1969), Carmen (1975), Frederick (1979), Alicia (1985), and Andrew (1992) have clearly shown the
devastating potential of these storms in the Gulf of Mexico. Even though shallow-water effects may diminish
coastal wave heights from the values listed in Table II-2-2, wave conditions are still sufficient to control
design and planning considerations for most coastal and offshore structures/facilities in the Gulf.
II-2-56
Meteorology and Wave Climate
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