Estimates of the duration of the wind are also needed for wave pre- 

 diction. Computer results, especially for short durations and high windspeeds 

 may be sensitive to differences of only a few minutes in the duration. 

 Complete synoptic weather charts are prepared only at 6-hour intervals. Thus 

 interpolation to determine the duration may be necessary. Linear inter- 

 polation is adequate for most uses, and, when not obviously incorrect, is 

 usually the best procedure. Care should be taken not to interpolate if short- 

 duration phenomena, such as frontal passage or thunderstorms, are present. 



The effect of fetch width on limiting ocean wave growth in a generating 

 area may usually be neglected since nearly all ocean fetches have widths about 

 as large as their lengths. In inland waters (bays, rivers, lakes, and 

 reservoirs), fetches are limited by landforms surrounding the body of water. 

 Fetches that are long in comparison to width are frequently found. It is not 

 clear what measure of width is important in limiting the growth of waves. 



1004 '9°° 996 



996 



000 



004 



1004 



1000 



1020 1016 



1012 



1012 



1006 



1020 1016 1012 1006 



1012 



016 



D 



Figure 3-20. Possible fetch limitations, 



3-41 



