seastate

Seastate, or sea state, refers to the condition of the surface of the sea at a given time, as determined by the height, period, and direction of surface waves, along with the prevailing wind and swell. It is a key parameter in meteorology and maritime operations because sea state directly affects navigation, offshore work, and coastal processes.

The most common quantitative measure of seastate is the significant wave height (Hs), defined as the average height of the highest one-third of the waves. Other important quantities include the mean wave period (the average time between successive crests) and the wave spectrum, which describes how wave energy is distributed across frequencies. Measurements come from ships, moored or drifting buoys, coastal stations, and satellite radar altimetry, and are integrated into forecast models to predict future conditions.

Qualitatively, seastate is described using descriptors such as calm, smooth, slight, moderate, rough, very rough, high, very high, and, in some scales, phenomenal. These terms are often correlated with ranges of Hs and wind speeds by meteorological services, though exact mappings can vary by region. Wind strength, wind duration, and fetch (the distance over water the wind blows) determine seastate, while swell generated by distant storms can influence conditions far from the wind source.

Impact and applications include navigation safety, vessel design and operation, offshore construction, search and rescue planning, and coastal management. Accurate seastate assessments support decision-making for crews, cargo handling, and recreational activities such as surfing and boating.