5.1.3. Hurricanes 
Hurricanes are tropical cyclones with wind speeds of 119 km per hour (74 mph) or higher that 
occur over the Atlantic Ocean, Caribbean Sea and Gulf of Mexico usually during summer and 
fall. These storms originate in warm waters in areas of low pressure and with wind circulation 
counterclockwise around the center. Hurricanes have struck South Florida half of the years 
during the past century, and the frequency of hurricanes is greater in South Florida than in any 
other place in the US (Gentry, 1984). The frequency of hurricanes in the Atlantic was below 
normal from 1894 through 1930, and was especially low from 1911 through 1921. During the 
1930s, the frequency increased above normal and remained so through 1982, with the 
exception of a few years around 1940. In Florida, the frequency was above normal from 1933 
- 1938, 1945 - 1952, and 1964 - 1966. Otherwise, frequencies have been slightly below 
normal. The increase in frequencies in the Atlantic area during the 1930s may be attributed to 
improved observations. In addition to the variations in frequencies for the Atlantic, there are 
periods in which the hurricane tracks seem to concentrate on Florida, for example 1945 - 
1950. During 1952 - 1957 and 1967, they seemed to shift away from Florida. 
Tropical storms passing over or within a radius of approximately 50 mi of Florida Bay from 
1910 to 1993 are listed in Table 9. The intensity of the storm on the Saffir/Simpson scale 
(Table 10) at the time it passed over or closest to the Bay is noted in Table 9. 
Meeder and Meeder (1989) described the effects of hurricanes on the Florida Bay ecosystem 
and contrasted them to the effects of fires in south Florida terrestrial ecosystems. Just as the 
importance of fires has been recognized in the management of terrestrial ecosystems, the role 
of hurricanes on coastal and shallow bay communities must also be recognized. Anthropogenic 
alteration of hurricane runoff quantity and timing, quality of runoff water and tidal exchange 
rates are possible. Intense periods of rapid runoff appear to be very significant in maintaining 
the Florida Bay ecosystem. Physical processes associated with hurricanes are: rainfall, storm 
tides, extreme wind and waves, and outwash. Although predicting the precise effects of any 
given hurricane is difficult, several observations were made after analysis of storm data since 
1971: (1) a total of 95 tropical storms have affected the Florida Bay ecosystem, and 20 of 
these were considered major storms; (2) nearly 50% of all the storms fell within three 
general tracts; (3) of 39 storms analyzed since 1916, rainfall from individual storms made up 
1.7 to 14% of annual rainfall; (4) storms from different vectors produced different rainfall 
characteristics; and (5) 11 storms from two vectors produced more than twice as much rain 
as other storms (averaging 213 mm). From these observations, two generalizations were 
made: storms that affect the Bay bottom and coastline occur at reasonably predictable 
intervals of one every 3 - 5 yrs, and storms which produce extreme freshwater runoff occur 
once every 6 to 7 yrs. 
Although Hurricane Andrew was a devastating storm for South Florida, the last major 
hurricane to significantly impact Florida Bay was Hurricane Donna. An excellent description of 
the effects of that storm on the Bay was prepared by Craighead and Gilbert (1962) and 
excerpts of this work are used in this section. 
