20 



Not so dramatic a change occurs in the afternoon winds 

 between the summer and winter. The principle change is a 

 shift to the northwest of the dominant winds during the summer 

 accompanied by a slight increase in velocity. This is the 

 result of the northward displacement of the permanent east 

 Pacific high pressure area in the summer season and shifts 

 the prevailing winds more or less parallel to the coast. 



Winds from the north and south are rare and insignificant 

 during all months. They are most noticeable in the winter 

 when they result from frontal activity. 



Winds of velocities greater than 30 knots are uncommon. 

 When they do occur, they are winter frontal winds or north- 

 west afternoon breezes of late summer and early fall. In 

 more than ten years of observations by the Catalina Island 

 steamers, only 4 days had winds with velocities greater than 

 Force 5 on the Beaufort scale. In each case they were north- 

 west winds. 



SEA AND SWELL 



Sea and swell are generated by winds and the differences 

 between the two are determined by the proximity of the areas 

 of generation to the region under consideration. An adequate 

 understanding of the origin of local sea and swell can only 

 be gained through knowledge of the meteorology involved. 



The northwesterly air flow and the southwestern thermal 

 low are the most important meteorological factors effecting 

 the formation of local wind waves. They control to a large 

 extent the movement of fronts and storm systems and are mainly 



