Period

In marine forecasting, period is the time interval, in seconds, between successive crests of waves or swell passing a fixed point. It describes the spacing and energy of the sea: a 6-second period is short and steep, while a 14-second period indicates longer, more powerful swell.

For boaters, period is as important as height because it affects comfort, speed and safety. Short-period seas can cause pounding, slamming and difficult steering, especially when wind opposes tide or current. Compare period with Wave Period, Swell Period and Sea State when assessing a route, bar crossing or anchorage.

PredictWind wave forecasts and GRIB data show period alongside wave height and direction, helping skippers judge whether conditions are manageable for their vessel. In Weather Routing, period helps identify uncomfortable or risky sea states before departure and supports better timing for offshore passages.