The plotted synoptic wave chart is used as an overlay on the 1230Z 

 synoptic weather chart. The analysis procedure is conducted on a light 

 table. First, the wave charts and associated weather charts are ex- 

 amined for the directions of the predominant wave trains which are then 

 indicated by heavy arrows. An examination of all ship observations is 

 made, and those observations which appear to be unreasonable are re- 

 jected. A few spot calculations are made for wave heights and periods 

 as a check on the order of magnitude of reported wave heights and periods; 

 this is especially important when very few ship observations are available 

 making it difficult to determine the reasonableness of a report. The cal- 

 culations are made using standard techniques i.e. Sverdrup-Munk (195>l) 

 Bretschneider (l9£l), and Pierson, Neumann, and James (1955)- The areas 

 which contain little or no ship observations must now be considered; for 

 these areas, wave heights and periods are calculated and plotted on the 

 wave chart. 



With the arrows indicating the predominant wave trains, and the iso- 

 baric pattern on the weather chart as a guide, contour lines of equal wave 

 height, based on the 1200Z ship observations, are sketched injthe 0600Z ob- 

 servations are used as a guide. The calculated wave heights are now examined 

 to see if they fall reasonably xrell within the order of magnitude of the 

 contour lines based on reported ship observations. The calculated wave 

 heights will generally show the relative heights fairly well. If the ab- 

 solute values appear to be off, the calculated heights are adjusted to fit 

 smoothly with the contours based on ship observations. There are no isolines 

 of wave period on the chart; this would add another set of lines to the chart 

 complicating it unnecessarily. In addition, it has been observed that re- 

 ported wave periods are not sufficiently reliable to draw reasonably good 

 isolines of wave period. Calculated wave heights are plotted for the points 

 which appear to be most necessary to fix the predominant features of the 

 wave chart and where ship observations are lacking. 



No detailed calculations are made for the coastal areas since it would 

 require considerable time and effort to take into consideration the shelter- 

 ing effects and limited fetches; reported coastal observations, however, are 

 taken into consideration. Calculations of nearshore wave conditions are 

 made only for specific forecast requirements which are usually very much 

 localized. The indicated procedure, in its present state of development,, 

 was designed to obtain a rapid evaluation of wave conditions over a large 

 ocean area with reasonably good accuracy. 



C. PROGNOSTIC WAVE CHART 



1. Principles 



There are undoubtedly many ways in which the problem of producing a 

 prognostic wave chart can be approached. The method outlined below is one 

 of many compromises, with the major considerations being speed of analysis, 

 considered as firmly established since at present the charts are not pro- 

 duced as a standard item for operational use, but rather as a basis for 

 further developmental work. 



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