D 



Nuiuerical value 



1^3 hours 



18.0 feet 



9.0 seconds 



600 naut . m. 



0.47 



8.3 feet 



1.27 



11.4 seconds 



40 hours 



690 feet 



35 knots 



When preparing a forecast on the basis of this analysis it 

 must be considered that the v.lnds over the distance of decay can be 

 expected to continue to blow in the direction of orogress of the 

 swell so that the decrease in height will be less than that obtained 

 from Plate "VI. Froia this prognosis of the v/eather conditions it is 

 estiiiiated that a following wind of 10 knots will be present over the 

 entire distance of decay. According to the procedure outlined above 

 (exaiiiple 1) the swell should then arrive with a height of 12.2 feet 

 and the period of the swell should remain unchanged, but this wave 

 height may be somev/hat high and the period may be too short. Fur- 

 thermore, the wind system causing the svjell v.dll probably continue 

 to advance towards the east so that the height of the sv^ell can be 

 expected to increase for some time as the distance of decay shortens, 

 The following forecast should therefore be issued; 



55 



