coast. Thus, after experience has been gained, The problem of forecasting changes of waves 



it is possible to forecast swell several days in in shallow waters and the height of breakers 



advance. Forecasts of the state of the sea, on and the amount of surf on any given beach is 



the other hand, must be based in part on prog- covered in separate manuals, H. 0. Pub. No. 



nostic weather maps and cannot be prepared 234, Breakers and Surf, Principles in Fore- 



for periods longer than those for which these CASTING, and H. 0. Pub. No. 605, Graphical 



maps can be considered valid. Construction of Wave Refraction Diagrams. 



