DIRECTION OF ADVANCE 



39 



Figure 6. — Simplified chart showing the isobaric distribution over the North 

 Atlantic at 1300, Greenwich mean time, September 19, 1938. 



so that the relationship between wind direction and wave direction to 

 be expected with the approach of a disturbance depends not only on 

 the shapes of the isobars within the latter, but also on the position of 

 the observer relative to its line of advance. The winds of tropical 

 hurricanes afford a classic example of this. In one such example in 

 the tropical North Atlantic (Tannehill, 1936, pp. 231-238), the direc- 

 tion of the wind is known to have deviated by as much as 60° from 

 that of the waves in the two front quadrants of the cyclonic disturb- 

 ance, and by as much as 90° to 100° in the left rear quadrant whereas 



