Hurricane Andrew (1992)

Hurricane Andrew was a small and ferocious Cape Verde hurricane that wrought unprecedented economic devastation along a path through the northwestern Bahamas, southern Florida peninsula, and south-central Louisiana (Rappaport 1993). The National Weather Service estimated the damage at $26.5 billion, making Hurricane Andrew the most expensive natural disaster in U.S. history as of 1992. In 2005, Hurricane Katrina ($81 billion) surpassed Hurricane Andrew as the costliest natural disaster (Blake et al. 2007). Hurricane Andrew hit southern Dade County, Florida, especially hard, with violent winds and storm surges characteristic of a category 5 hurricane. Maximum sustained windspeeds of 141 miles per hour (227 kph), with gusts of 169 miles per hour (272 kph), were recorded on 24 August 1992 just before landfall in Florida. A storm surge of about 17 feet (5.2 m) above sea level was recorded at Biscayne Bay, Florida, and about 9 feet (2.7 m) near Terrebonne Bay in south-central Louisiana (Lovelace and McPherson 1998). The storm’s central pressure (922 millibars) ranks as the fourth lowest on record for a hurricane at landfall in the United States (Blake et al. 2007).

At the time, Hurricane Andrew was the first major hurricane to affect the Florida peninsula in more than 25 years. Hurricane Donna (1960) had been the last major storm to pass directly over the south Florida peninsula. Furthermore, between 1965 and 1992 only two hurricanes of any significance affected the state: (1) Hurricane Elena, a category 3 that eventually made landfall in Mississippi, and (2) Hurricane Kate, a late season, borderline category 1–2 storm. Both affected Florida within weeks of each other in 1985. In the 30 years preceding Hurricane Andrew, Florida experienced increased coastal and suburban development and population growth. By 1992 the demographics of central and south Florida had changed with many residents relocated from areas in the Northeast and upper Midwest. Thus a significant portion of the Floridian population in 1992 had little or no direct experience with Florida’s history of violent hurricanes, a fact that worried many forecasters at the time (Rappaport 1993).

Considering the destruction caused by this hurricane and the inexperienced population, the direct loss of life (< 25) seems remarkably low. However, more than 250,000 people were left homeless, 82,000 businesses were destroyed or damaged, and about 100,000 residents of south Dade County permanently left the area in Andrew’s wake. Hurricane Andrew also had a severe impact on the environment as it passed through the heart of the largest wetland in the United States—the Florida Everglades. Perhaps the most dramatic effect of the storm’s passage through these wetlands was the major structural damage to trees caused by the strong winds. The storm passed directly over Biscayne and Everglades national parks, knocking down or severely damaging mangrove trees on about 70,000 acres (28,329 ha) of wetlands. Mangrove and other wetland tree species are important to the aquatic and dry land parts of the park environment: they are instrumental in absorbing the force of hurricanes and they help build land by trapping silt and sand in their roots. These roots provide shelter and protection for a host of marine organisms, especially the very young and small, while the tree branches above provide breeding and nesting areas for many birds. Decomposing leaves and other plant material serve as food and provide nutrients to the water.

Within the storm’s path, virtually all large trees located in hammock areas (islands of dense, tropical undergrowth), typically hardwoods, were defoliated and about 25% of the trees were windthrown or badly broken. About one-fourth of the royal palms and one-third of the pine trees in Everglades National Park were broken or damaged by the winds (Lovelace and McPherson 1998). By contrast, the hurricane had little effect on wildlife in the Everglades. Thirty-two deer (Odocoileus virginianus) wearing radio collars for a National Park Service study survived the hurricane, and the re-leafing of vegetation, which occurred within 20 days on surviving trees and shrubs, provided the deer with food and cover. Adult alligators (Alligator mississippiensis) appeared unaffected, though nests and young may have been adversely impacted. Most wading birds survived (Davis et al. 1993).

In the marine environment, the major effects of the hurricane were changes in nearshore water quality, patches of intense bottom scouring, and beach overwash. Dramatically increased turbidity persisted in some areas for at least 30 days, particularly in western Biscayne Bay where mangrove peat soils continued to break down and enter the water. In northeastern Florida Bay, at the southern edge of the affected area, concentrations of ammonia, dissolved phosphate, and dissolved organic carbon increased dramatically. Blooms of phytoplankton (microscopic drifting aquatic plants) added to the increased turbidity and, combined with low dissolved-oxygen concentrations, affected fish and invertebrate populations. In addition, fuel from hundreds of damaged boats and marina fuel tanks in Biscayne Bay continued to discharge into the water for at least 27 days after the hurricane had passed (Davis et al. 1993).

Related Links

• NPS—Coastal Geology
• NPS—Coastal Geohazards
• NPS—Geology
• NPS—Oceans