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origin, but have dissipated long before reaching southern 

 California. Nevertheless, some send swell toward the coast 

 with a period of 9 to 11 seconds. This swell differs from 

 the southern hemisphere swell in having a shorter period. 



Data available indicate that the frequency of occurrence 

 of these storms is quite low. Six cyclones annually was the 

 average for 30 years determined by Nicholson, et al. (1946) 

 with an extreme of 14 for a single year. September is the 

 month when most of these occur. By the time the storms reach 

 the latitude of southern California they usually have utilized 

 a great deal of their initial energy and the surface winds are 

 not of the high velocities often associated with hurricanes. 



Although data were incomplete, Nicholson, ejt al. hazarded 

 the following comments concerning this source of swells "Over 

 a period of forty years only one typhoon, that of September 

 1939, entered southern California waters with high wind 

 velocities and caused significant damage due to wind waves. 

 Waves from a similar storm, if and when one arrives again, 

 will undoubtedly be the most severe affecting the area. 

 Unfortunately, the height of the typhoon waves, the direction 

 of their approach to the beach, and the strength and direction 

 of the longshore currents under such conditions cannot be 

 estimated." 



Without additional data the estimate of one occurrence 

 every four or five years cannot be modified, but the possibility 

 should be entertained of a frequency as high as once a season. 

 There is no indication that these waves always arrive with 

 destructive heights. On the contrary, they will often be low. 



