F0RECA3TIKG OF WAVES FOR SHORT FETCHES 



In areas such as the Mediterranean and other partially enclosed 

 bodies of water, it is often necessary to forecast waves generated 

 over short fetches which are dsterioined entirely by coast lines and 

 wind direction. In this case the problem of forecasting becomes 

 primarily a iiieteorological problem of forecasting the direction and 

 velocity of the wind. If this can be done, the wave height and wave 

 Deriod are found from Plate III if the fetch is shorter than 100 

 nautical miles, and from Plate II if it is longer. The duration is 

 rarely limiting if the fetch is less than 200 nautical miles, but 

 should such be the case Plate IV or V must be used. 



Example 



A strait running north-south has a width of 30 Ldles. At 12^0 

 it is forecast that a northv/est wind will reach the strait, will 

 attain a velocity of 30 knots at 2000 and will continue to blow 

 vi'ith that velocity for 12 hours. What waves can be expected off 

 the eastern shore of the strait at 0600 the next morning? 



The pertinent values are: 



Fetch 43 naut. m. 



Wind velocity 30 knots 



Duration, 20^0 to 0600 10 hours 



Kinimum duration 6 hours (Plate I) 



Since the duration is longer than the minimum duration Plate II is 

 used, from which 



H = 9.5 feet, T = 5.0 seconds 

 36 



