80 



FREQUENCY OF WAVE CONDITIONS 



The increasing frequency through the autumn of high seas over 

 the northern part of the North Atlantic is further reflected in the fact 

 that most of the area of the latter is disturbed by a swell of 12 feet 

 or higher for more than one-tenth of the time by the last part of the 

 winter. The only exceptions are along the Lesser Antilles, the 

 Bahamas, and northern Cuba in the west, also the subequatorial belt 

 in the east, from equatorial West Africa out to the longitude of eastern 

 Brazil, where a high swell, like a high sea, has not been reported at 

 all in January and February for some of the 5° squares, nor in fre- 

 quencies greater than 6 or 7 percent for any of the others. To the 

 northward, indeed, of the Northeast Trades, it is only off the coasts 

 of Florida, Bahamas, and Cuba that the swell has been reported "low" 

 or altogther absent for as much as 60 percent of the time in late winter ; 

 whereas in August this applies not only to the entire western side of 

 the North Atlantic, west of the longitude of Newfoundland, but also 

 to an extensive area as well in midlatitudes in midocean (pi. IV). 



A longitudinal contrast, of practical interest in the state of the 

 swells of winter, is that these are considerably less often high along 

 the coast of the northeastern United States and off the coasts of Europe 

 and of northwest Africa than they are in midocean, as is illustrated 

 by table 20. 



High swells are somewhat more common in the Gulf of Mexico in 

 winter ( 4 to 9 percent) than at the end of the summer (0 to 5 percent) ; 

 likewise, they are considerably more common throughout the Carib- 

 bean as a whole, much as high seas are (p. 79), and with similar 

 gradation, with frequencies from about 5 percent under the immediate 

 shelter of the Antilles in the east but 11 to 20 percent along the coasts 

 of Colombia and of Nicaragua in the west. 



Table 20.— Ranges of percentage frequencies of high swells in unit areas of the 

 North Atlantic in January and February, to shoiv the contrast between the frequency 

 of high swells within approximately 500 miles of the American and European 

 coasts and thai in midocean 



SOUTH ATLANTIC 



Available data suggest that a really high sea is about as common in 

 high latitudes of the one hemisphere as of the other during the stormy 



