86 FREQUENCY OF WAVE CONDITIONS 



Agreement between the two classes of waves is also close in the east- 

 ern side of the tropical Pacific, from the Equator northward coastwise 

 to southern California. 



Perhaps the difference chiefly deserving of emphasis between the 

 August picture for swells for the North Pacific and that for seas 

 (since it might not appear from a cursory survey of the respective 

 charts) is that a high swell has been reported more than 10 percent 

 (locally as often as 38 percent) of the time, between the Equator and 

 latitude 5° N., westward from the Galapagos Islands, where a high 

 sea has not been reported at all in any of the returns for the month. 



The swell is reported as more commonly high in the southern part 

 of the Sea of Okhotsk (20 percent) than the sea is (0 percent high) 

 and less commonly low there. A high swell is also reported somewhat 

 more often (11 to 19 percent) than a high sea (9 to 13 percent) in the 

 eastern and southeastern parts of the South China Sea. But there is 

 no great difference in the frequencies with which high swells and 

 seas are reported near the Asiatic mainland in this region (0 to 10 

 percent for swells, 1 to 14 percent for seas). Neither is there any 

 greater difference in the relative prevalence of low swells in summer, 

 as compared with low seas, either for the South China Sea or for the 

 Japan Sea, than can be charged to the fact that this category includes 

 a much wider height range for swells than for seas (p. 71) . 



Winter. — The sea is much more commonly rough in middle and high 

 latitudes of the North Pacific in winter than it is in summer, as might 

 be expected from the stormier weather; in fact, it has been described 

 as "high" in 40 to 60 percent of the late winter reports that have been 

 received, not only across the Alaskan bight, but throughout most of 

 the northwest part of the Pacific down to latitude about 30° N., ex- 

 cept along the Japanese island chain, where it is high rather less often 

 even at this time of the year (12 to 36 percent). Ships crossing from 

 Yokohama to Seattle or Vancouver may thus expect a rough sea some- 

 thing like half of the time, except, perhaps, as the American coast is 

 neared, and even higher than 20 feet during winter gales, according 

 to evidence from other sources. 27 And winter crossings from Japan 

 to San Francisco are also likely to be rough, after the first couple of 

 hundred miles and until the longitude of the eastern Aleutians has 

 been left behind, after which it is likely to be smoother, especially 

 nearing the California coast, where a high sea has been reported only 

 about 10 to 14 percent of the time, even in winter. 



The most widespread evidence, however, of the increasing rough- 

 ness of the North Pacific, through the autumn, is that the boundaries 



* The reported frequency of 10 percent, for seas higher than 20 feet, south of the Alaskan 

 Peninsula in the latitude of Oregon (p. 21), is for the year as a whole; actually, however, 

 so heavy a sea is encountered much more often in high latitudes of the Pacific in winter 

 than in summer, just as it is in the Atlantic. 



