total sample and the subsample was 4.8 seconds (o = 1.4 and 1.3). These 

 values indicate that there is no significant difference between the two 

 data sets, and suggest that comparisons of data collected from the three 

 sites are valid. 



A second consideration is the fact that the study was made during an 

 interval of 4.5 years in an area where a hurricane is expected only once 

 in 6 years and a tropical disturbance only once in 3 years. Although such 

 storms have not been considered as destructive to the southeast Florida 

 beaches as winter northeasters (UoS. Army Engineer District, Jacksonville, 

 1968), their effect on beaches has not been quantified, and is probably 

 significant. No hurricanes passed within 300 miles (483 kilometers) of 

 the three sites during the study. Three tropical disturbances passed 

 within a 50-mile radius. 



2. Winds and Storms . 



Monthly wind roses summarizing data from this study are plotted for 

 each site in Figures 23, 24, and 25. Winds are predominantly onshore 

 with speeds ranging from 8 to 15 miles per hour. Winds from the south- 

 east occur the greatest percentage of time and prevail during March 

 through August. Higher velocities are associated with northeasterlies 

 which occur mainly during September through February. The strongest off- 

 shore winds occur during the winter months (November through March) and 

 are predominantly from the northwest. There is little difference between 

 the annual averages for the three sites, except that Jupiter has a greater 

 occurrence of northerly flow. 



In general, the LEO wind data confirm the West Palm Beach wind data 

 summarized in Figure 9. The annual wind rose from Boca Raton (Fig. 23) 

 indicates onshore winds 66 percent of the time (see App. D for monthly 

 averages per year); the West Palm Beach data indicate onshore winds 57 

 percent of the time. Both sets of data confirm the predominant southeast 

 wind direction. The Boca Raton data indicate approximately 9 percent of 

 the onshore winds are less than 4 miles (1.6 kilometers) per hour; the 

 West Palm Beach data indicate that approximately 22 percent of the on- 

 shore winds at that island site are 5 miles (8 kilometers) per hour or 

 less. 



Although no hurricanes occurred within the study period, at least 

 one hurricane (Agnes) did affect the local weather system as it moved 

 northward over the Gulf of Mexico. Southerly winds of 15 to 17 miles 

 (24 to 27 kilometers) per hour were recorded at Boca Raton and Hollywood 

 as Hurricane Agnes passed some 350 miles (560 kilometers) to the west on 

 20 Jiine 1972. 



Gale-force winds were observed only once--during the 22 to 25 Decem- 

 ber 1971 northeaster at Jupiter, when a windspeed of 40 miles per hour 

 was recorded. A windspeed of 30 miles (48 kilometers) per hour was 

 measured during the same storm at Boca Raton. At least four tropical 

 storms or tropical depressions passed within 100 miles of the study area. 



39 



