74 FREQUENCY OF WAVE CONDITIONS 



cent). We cannot offer any explanation for this contrast, since gales 

 are not reported any more often near the African coast at this season 

 than they are farther to the westward ; neither do the Trades commonly 

 blow any more strongly there, nor more constantly in the one direction. 



The seas average somewhat lower toward either boundary of the 

 Northeast Trades than along the axis of the latter, as might be ex- 

 pected from the character of the wind; this is especially true along 

 the northern Bahamas and toward the coast of southern Florida, 

 where the sea has been described as "low" in 75 to 80 percent of the 

 August reports, and only very seldom as "high". And this applies 

 equally to the Gulf of Mexico (seas 70 to 80 percent low, to 1 percent 

 high). The Gulf is in fact as smooth as, or perhaps even smoother 

 than any subdivision of the open Atlantic of equal extent at this 

 season. 



The reader might reasonably object, here, that neither the foregoing 

 account nor the charts (pis. I and II) give any hint of the fact that 

 high and very dangerous seas do accompany the tropical hurricanes 

 that occur from time to time at this season, some of them crossing the 

 Caribbean and the Gulf of Mexico, but others skirting the West Indies, 

 Bahamas, and Florida, either to spend their force inland, or to run 

 parallel to the coast of the United States northward and northeast- 

 ward. The reason they do not more evidently influence the frequency 

 with which "high" seas are reported, is that really severe storms of 

 this nature are rather unusual events, even in the regions where they 

 occur the most commonly in the month in question. Thus the total 

 number of storms of this kind, of hurricane force, that were recorded 

 for August from 1887 to 1936 was only 51 (Tannehill, 1938, p. 113), 

 or about 1 per year, corresponding to which the percentage of severe 

 gales is shown on the Pilot Chart for August as only to 1 for the 

 region in question. 26 



The great frequency with which the seas are low (more than 40 

 percent) and the infrequent occurrence of high seas (0 to 7 percent) 

 are the outstanding features of the wave pattern of summer along the 

 belt of variable winds in the western half of the ocean, between the 

 northern boundary of the Trades and about latitude 40° N. 



The scarcity of high seas anywhere along the United States coast as 

 far north as the Grand Banks of Newfoundland (0 to 5 percent) in 

 summer is due to the fact that onshore winds, or longshore winds, 

 strong enough and with a fetch long enough to generate waves of any 

 considerable size are not usual there at this time of year. And it is 

 this prevailing smoothness of the sea, combined with the great num- 

 ber of good harbors, that makes our northeastern coast the summer 



*'The tracks of many of these cyclonic storms are laid down on the U. S. Hydrographic 

 Office Pilot Charts for August and for September, as well as for other months. 



