94 FREQUENCY OF WAVE CONDITIONS 



end of May until early in August, when the more venturesome put to 

 sea again. 29 The sea is also higher than 2 or 3 feet more constantly 

 (more than 80 percent) in this part of the Arabian Sea, during the 

 height of the Southwest Monsoon, than happens at any season any- 

 where else in the Indian Ocean, except in the western part of the South- 

 east Trades Belt, off Madagascar. 



The violent winds of the tropical cyclones that develop from time to 

 time in the Arabian Sea, and in the stfuthern or central parts of the 

 Bay of Bengal, are a second potential source of high and dangerous 

 seas in the northern part of the Indian Ocean. In the Arabian Sea 

 these occur most often during the period of transition between the two 

 monsoons, June through July and October. through November, but 

 they are infrequent even then. And while they cross the Bay of 

 Bengal most often from June through November, this does not happen 

 frequently enough to have any appreciable effect on the frequency with 

 which high seas have been reported there ; the total number of tropical 

 cyclones reported for the Bay of Bengal in July and August was only 

 92, for a 25 -year period, according to a recent tabulation. 30 



Transition is abrupt, in summer, from the stormy waters of the 

 Arabian Sea through the Gulf of Aden, into the Red Sea, to which 

 the monsoon does not extend, and where the winds of summer average 

 so light (8 to 10 miles per hour) — and with gales practically unknown 

 — that the sea rises only occasionally there to 9 feet. A high sea has, 

 however, been reported rather more often in summer in the Persian 

 Gulf (7 to 8 percent in July and August), for what reason is not 

 apparent, since the wind averages no stronger (less than 10 knots) and 

 gales are no more frequent there in summer than in the Red Sea. 



A high swell is reported at least as often as a high sea throughout 

 the North Indian Ocean as a whole during the Southwest Monsoon 

 season, excepting only along the Burmese coast of the Bay of Bengal 

 (pi. XIX). 



The contrast in frequency between the two classes of waves is par- 

 ticularly instructive in the northern part of the Arabian Sea, where 

 the high seas generated to the southward, where the monsoon average 

 strongest, assume the characteristics of swells so soon, as they spread, 

 that the latter are reported "high" considerably more often along the 

 coasts of northwestern Hindustan, of Beluchistan, and of Arabia in 

 July and August average about 40 percent) than the sea is (average 

 about 20 percent). Similarly, the swells of summer run high about 

 twice as often in the western side of the Bay of Bengal, northward 

 from Ceylon (average about 18 percent) as the sea does (average 



28 British Admiralty, West Coast of Hindustan Pilot, 4th Edit., 1898, p. 38. 

 30 Doraiswaniy Iyer, V. 1936. Typhoons and Indian weather. Mem. India. Meteorological 

 dept. vol. 26, p. 97. 



