Tertiary Swell

Tertiary swell is the third most significant swell train affecting a sea area, ranked behind the primary and secondary swell by height, energy or forecast prominence. It has its own wave height, direction and period, often arriving from a separate weather system and crossing over local wind waves.

Although usually smaller, tertiary swell can still affect comfort, safety and boat handling when it combines with Primary Swell, Secondary Swell or a steep local Sea State. Crossed swell patterns may increase rolling, slamming, crew fatigue, fuel burn and the risk of gear movement, especially on beam or quartering angles.

In PredictWind wave forecasts, reviewing each swell component helps you understand the full motion your vessel may experience, not just the dominant wave. Compare swell direction, height and period with your intended heading, anchorage exposure and Weather Routing options before committing to a passage.