The character of the significant waves in a generating area can be 

 obtained from the Scripps charts provided the variables of wind velocity, 

 fetch, and duration are known „ In lakes or protected bays, local wind 

 records are suitable for estimating the wave conditions that can exist at 

 any particular locality „ In fact, all past wind records of velocity, 

 direction, and duration can be used in conjunction with the charts and a 

 statistical compilation then made of the anticipated wave conditions at a 

 selected point These data on wave heights then can be summarized in the 

 form of direction roses „ Information of this type is of considerable 

 value to the designing engineer, as it not only gives the wave character- 

 istics which structures must be designed to withstand, but it also permits 

 an investigation to be made as to whether structures are economically 

 justified in view of the frequency of occurrence of waves of a damaging 

 character o 



For a locality on an exposed coast, where critical wave conditions 

 result from swell which is generated by storms occurring at considerable 

 distance from the coast, local wind records are of relatively small value 

 in the compilation of significant wave characteristics , Thus, where large 

 scale wind patterns are involved, there are seldom sufficient weather 

 reports to determine these patterns directly from ship or island ob- 

 servations o However, there is a very close relationship between the speed 

 and direction of the wind and the atmospheric pressure gradiento This 

 latter factor can be determined from a weather chart „ The pressure field 

 is not difficult to determine, even from only widely scattered reports,, 

 The winds, therefore, are computed from the pressure gradient scales from 

 a weather chart and whatever wind observations are available are used to 

 check the computed values „ A consideration of the orientation of the 

 isobars on a weather chart also permits an estimate to be made of the 

 extent of the generating area and, consequently, the value of the fetch 

 and the direction of wave propagation By these methods of forecasting, 

 a statistical study can be made of the waves reaching a region of the 

 coasto Such an analysis has been made by the Scripps Institution of 

 Oceanography in cooperation with the Los Angeles District for Pacific 

 coast stations „ The results of the studies have been compiled into wave 

 "roses" for five stations located along the Pacific coast at approximately 

 150 mile intervals from San Diego, California, to Cape EELanco, Oregon „ 

 These statistical summaries, Figure 4., give wave conditions in deep water 

 and are basic data in the design of all future works on this portion of 

 the coasto 



The use of weather charts in estimating wave conditions at a par- 

 ticular locality can be used to advantage by engineers involved in con- 

 structing coastal works or in using floating equipment which is ex- 

 posed to wave action o Although engineers usually plan their immediate 

 work on the local weather reports, in many cases it is the swell, coming 

 from storms occurring several days previously at a distant locality, 

 which actually affects their operations „ A 24-hour forecast of wave con- 

 ditions that might exist at a particular point for a short time in the 

 future would be of unquestioned value to the construction engineer „ 

 Usually it is not possible to make a reliable forecast for more than two 

 days in advance „ The details of utilizing daily weather charts for making 



