18 



directions. However, for 33% of the year (120 days) the wind 

 was from either the west or southwest, and from the duration 

 of wind in days and the wind movement in miles, a prevailing 

 wind from the southwest is indicated. These data do not show, 

 though, the land breeze which is the dominant air motion in 

 the morning hours throughout most of the year. 



From information taken aboard the Catalina Island steamers, 

 the S. S. CATALINA and the S. S. AVALON, wind directions and 

 velocities have been compiled for morning and afternoon for 

 each month. Even though the reporting station is approximately 

 8 miles south of San Pedro, a check with the winds obtained 

 during 1955-56 aboard the VELERO IV in Santa Monica Bay show 

 there to be no detectable variations other than those to be 

 expected from year to year. These winds from the San Pedro 

 Channel are shown in Figure 6. 



During the later fall and winter months the morning is 

 dominated by winds from the northeast and southeast while in 

 the afternoon, west and northwest breezes prevail. In the 

 spring, summer, and early fall, the morning northeast breeze 

 is almost nonexistent and although the southeast wind con- 

 tinues to occur, its velocity is much lower. This change in 

 the morning land breeze is due to the differential heating of 

 the land during the summer and winter seasons. Because of the 

 high temperatures over southern California in summer, a sea 

 breeze blows at nearly all hours and the night cooling effect 

 is shown mainly be a decrease in velocity of the sea breeze. 

 It may also cause the sea breeze to cease blowing in the 

 morning, this being indicated by the increase in calm mornings 

 in the summer. 



