Wave measurement data acquired over more than two decades along the coasts of Japan and the Pacific coast of USA are analyzed from three points of view (1) year-to-year variation, (2) jumps and (3) trends for wintertime- and summertime-meanvalues of significant wave height and period. Main findings are as follows:(1) the winter of 1998, containing the severest El-Nino period, gives the highest mean wave height along the western Pacific coast of Japan and the Pacific coast of USA.(2) a seesaw-like variation with a two-year period of season-separated meanwave heights along the Pacific coast of Japan may be observed and (3) one jump and an increasing trend in summer-time mean wave period data may be observed along the coasts of Japan.
