25 



these depressions may, at times, dispatch swell to the 

 California coast, where it arrives with periods of 12 to 15 

 seconds from the westsouthwest , and with moderate heights 

 (usually less than 8 feet). This type of storm occurs most 

 frequently and with the greatest strength in the spring, 

 although examples have been known throughout the year,, The 

 approximate frequency must give an annual average of about 

 one storm a month, but with an irregular season distribution 

 and from year to year. 



Swell from these Hawaiian Lows arrives in Santa Monica 

 Bay from between 22 5° and 280° with a period between 11 and 

 15 seconds. 

 Generation Areas in the Southern Hemisphere 



Wave observations at the Scripps Institution of Oceano- 

 graphy indicate that swell often arrives from a bearing 

 between south and southsoutheast and has an exceptionally 

 low period of from 13 to 20 seconds. It is believed that 

 this swell comes from generation areas in extratropical 

 cyclones moving from west to east across the South Pacific 

 Ocean between Australia and Chile. The lack of synoptic 

 weather observations in that part of the world eliminates 

 verification of this possibility (Nicholson, Grant, Shepard, 

 and Crowell, 1946). However, the direction of wave travel 

 leads either to an assumption of this source, or to consider 

 it as having been generated by tropical storms. This last 

 possibility is eliminated for the longer swell since the 

 observed period at the California coast indicates a travel 

 distance from 3,000 to 4,000 miles. The duration, fetches, 



