When data are not available for a specific beach, the wave climate 

 can be estimated by extrapolating from another location, after correcting 

 for differences in coastal exposure, winds, and storms. 



On the east, gulf, and Great Lakes coasts, local winds are often 

 highly correlated with the direction of longshore currents. Such wind 

 data are available in "Local Climatological Data" sheets published monthly 

 by the National Weather Service, National Oceanographic and Atmospheric 

 Agency (NOAA) for about 300 U.S. weather stations. Other NOAA wind-data 

 sources include annual summaries of the Local Climatological Data by sta- 

 tion (Local Climatological Data with Comparative Data), and weekly sum- 

 maries of the observed weather (Daily Weather Maps), all of which can be 

 ordered from the Superintendent of Documents, U.S. Government Printing 

 Office, Washington, D.C. 20402. 



Local weather data are often affected by conditions in the neighbor- 

 hood of the weather station, so care should be used in extrapolating 

 weather records from inland stations to a coastal locality. However, 

 statistics on frequency and severity of storm conditions do not change 

 appreciably for long reaches of the coast. For example, in a study of 

 Texas hurricanes, Bodine (1969) felt justified in assuming no difference 

 in hurricane frequency along the Texas coast. In developing information 

 on the Standard Project Hurricane, Graham and Nunn (1959) divided the 

 Atlantic Coast into zones 200 miles long and the gulf coast into zones 

 400 miles long. Variation of most hurricane parameters within zones is 

 not great along straight open stretches of coast. 



The use of weather charts for wave hindcasting is discussed in Sec- 

 tion 3.4. Computer methods for generating offshore wave climate are now 

 (1973) under test and development. However, development of nearshore 

 wave climate from hindcasting is usually a time-consuming job, and the 

 estimate obtained may suffer in quality because of the inaccuracy of 

 hindcast data, and the difficulty of assessing the effect of nearshore 

 topography on wave statistics. At the present time, if available at the 

 specific location, statistics based on wave-gage records are preferable 

 to hindcast statistics when wave data for the shallow-water conditions 

 are required. 



Other possible sources of wave climate information for office stud- 

 ies include aerial photography, newspaper records, and comments from 

 local residents. 



Data of greater detail and reliability than that obtained in an 

 office study can be obtained by recording the wave conditions at the 

 shoreline locality for at least 1 year by the use of visual observers 

 or wave gages. A study of year-to-year variation in wave height statis- 

 tics collected at CERC wave gages (Thompson and Harris, 1972), indicates 

 that six observations per day for 1 year gives a reliable wave height 

 distribution function to the 1 percent level of occurrence. At the gage 

 at Atlantic City, one observation a day for 1 year provided a useful 

 height-distribution function. 



4-36 



