Secondary Swell

Secondary swell is a distinct swell train arriving from a different direction, period, or source than the dominant swell. In marine forecasts it is usually smaller than the primary swell, but it can still influence motion, comfort, and breaking conditions.

For boaters, secondary swell matters because crossing wave trains can create a confused, lumpy Sea State, increase Roll, and make steering or sail trim less efficient. Comparing its height, direction, and Swell Period helps identify uncomfortable beam-on seas, hazardous bar entrances, or routes where waves oppose tide or current.

PredictWind wave forecasts separate primary, secondary, and tertiary swell so you can see more than a single combined wave height. Use wave maps, tables, and routing tools alongside wind forecasts to choose safer departure windows and optimise course angles, especially offshore or when swell systems are crossing a coastal passage.