Figures 37 to 40 give percent frequency of wave heigiit, period, and wave direction 

 for winter (Jan-Mar), spring (Apr-Jun), summer (Jul-Sep), and fall (Oct-Dec), respectively, 

 for the northern sector (30° to 45°N) of the survey area. During the winter months the 

 frequency of high seas (>3.7 meters) increases from south to north and from east to west, 

 showing a maximum of 15 percent in the northwest and a minimum of about 2 percent off 

 southern California. The prevaiUng southwest to west winds, reflecting the steep pressure 

 gradient between the Aleutian low and the north Pacific high, generate high frequencies 

 (>50 percent) of seas 1.5 meters or higher in the west. These decrease substantially towards 

 the east. 



During May, seas of 1.5 meters or higher are at a maximum frequency (near 50 per- 

 cent) at 30° to 35°N and 120° to 130°W. The summer months represent the period of 

 lowest sea state for the entire area. However, the winter trend is reversed ; the wave heights 

 tend to increase slightly toward the east with the area of maximum frequency of 1.5 meters 

 or greater seas being located about 35° to 40°N and 125° to 130°W. Waves of 3.7 meters or 

 higher are observed with frequencies of 2 percent or less in all areas. During the fall, the sea 

 state begins to increase toward winter values. 



Wave heights of at least 1 meter will probably be necessary for wave-powered pumps 

 of economical size. Figures 41 and 42 give persistence graphs for wave heights of 1 meter or 

 greater at OWS N and P, respectively (see Fig. 30 for map). They give percent frequencies 

 of the duration of events and days interval between events. At both weather stations there 

 is a maximum of approximately 5 days between events ( 1 00 percent of the waves > 1 meter 

 were followed by another such condition within 5 days). 



The median duration of waves > 1 meter is about 50 hours in the summer and over 

 200 hours in the winter at OWS N, and 24 hours both summer and winter for OWS P. Fig- 

 ures 43 and 44 give persistence graphs for high seas (>5 meters) for OWS N and P, respec- 

 tively. At OWS N waves >5 meters are rare or nonexistent during May through September. 

 The rare occurrence in August is probably due to occasional tropical cyclones. During fall 

 and winter the median duration of high seas is between 6 and 12 hours and the median 

 interval is between 8 and 16 days. For OWS P, high seas are more frequent, with the median 

 duration being similar (6-12 hours), but the median interval is reduced to 1 to 2 days in 

 winter or fall and 40 to 48 days in summer (June, July). 



In the southern portion of the survey area sea and swell are caused by the northeast 

 trade winds. During winter and fall these winds blow from 5° to 25° N and during spring 

 and summer they blow from 10° to 30°N. Southeast trades are important in producing sea 

 and swell in the southeast section during spring and summer. 



The frequency of seas greater than or equal to 1 .5 meters in height is generally great- 

 er in the western portion of the survey area because of the long northeast fetch. Figures 45 

 and 46 give the percent frequency of wave height, period, and direction characteristics for 

 winter and summer for the southern portion of the survey area from 30°N to 0°. During 

 the winter and spring, seas are normally from the northeast. South of 5°N the seas are 

 generally from the southeast to east because of the southeast trades. The seas become calm- 

 er as the coast is approached, with the southeast being the calmest portion due to the short 



25 



