waves to the state of the sea as described by a scale such as the 

 Douglas Sea Scale. 



This manual deals with the generation of waves by wind and 

 vj-lth the travel of waves in deeio water after they have left the 

 regions of strong winds. Methods are described for deteriuining 

 the characteristics of wind waves by neans of data froja adequate, 

 consecutive synoptic v/eather laaps and for forecasting swell off 

 coasts. 



Relationships between vv^aves and the three iiiiportant variables, 

 wind at the sea surface , fetch (the stretch of water over which the 

 vand blows) , and duration (the length of time the wind has blovm) 

 are discussed. Verifications and interpretations of the enpirical 

 laws developed by various observers of waves are given, together 

 with graohs for use in forecasting wind waves and sv^'ell. 



In order to use the graphs uiost effectively their r)hysical 

 significance and limtations nust be clearly understood. Forecasts 

 should therefore not be attempted until the forecaster has studied 

 the first part of the paper wl^ich describes the processes leading 

 to the groA/vth and decay of waves. 



Tests of the uethod made to date indicate that swell forecasts 

 can be made with about the same certainty as that of Most meteor- 

 ological forecasts. Prognostic charts are not important for the 

 forecasting of sv/ell because considerable time elapses between t^ e 

 generation of waves in distant storm areas and their arrival at the 

 coast. Thus, after experience has been gained, it is possible to 

 forecast swell several days in advance. Forecasts of the state of 

 the sea, on the other hand, must be based in part on nrognostic 



