The seasonal characteristics of wind duration around Japan are analyzed to estimate the wave encountered during the navigation for the safety at sea. Analyses are made on the basis of every 3-hour wind data of 10 years at 31 locations around Japan. The seasonal mean cumulative occurrence rates of constant direction wind, which are obtained by adding the occurrences from longer wind duration, decrease exponentially with wind duration. The seasonal mean cumulative occurrence rates of constant speed wind and constant direction and speed wind decrease to the minus power of wind speed with wind speed. The seasonal mean cumulative occurrence rates of wind blowing continuously more than certain wind speed criteria decrease exponentially with wind duration. There are recognized to exist the seasonal differences of the characteristics of wind duration. The seasonal characteristics of wind duration have some relationships proportional to seasonal mean wind speed. It is proposed how to estimate their seasonal characteristics of wind duration by using them.
