This article explores the factors that affect the roughness of the Sea of Japan, how to measure it, and some examples of stormy conditions in the area. Weather, tides, ocean currents, temperature changes, salinity differences, upwellings from deeper waters and wave heights due to swell are all discussed as factors that interact with each other to create different levels of turbulence or calmness in different parts of the sea. Examples of storms in the area include typhoons during summer months along coastal regions; winter storms off Hokkaido Island; and tropical cyclones off Okinawa Island. Wave buoys are used to measure wave heights and directions over long periods for accurate data points.