Forecast guide

Primary swell, secondary swell and wind sea

Marine models often split the ocean surface into several components. That matters because a clean groundswell and short local wind sea can exist at the same time, and they create very different surf.

Primary swell is usually the main surf signal

The primary swell is the dominant organized wave train in the model. When it has enough height, longer period and the right direction, it is often the component surfers care about first.

SwellOracle prioritizes primary swell for model-point alerts when that component is available, because it is usually more useful than a mixed total-wave value.

Secondary swell can matter when directions differ

Secondary swell can be smaller but still important if it comes from a direction your spot receives better than the primary swell. It can also add cross energy and make conditions less organized.

If the primary swell looks strong but the beach is not responding, check whether the direction is wrong and whether a smaller secondary swell is actually the visible one.

Wind sea is often noise for surf alerts

Wind sea is generated by local or regional wind and usually has shorter period. It can raise total wave height while still producing weak or messy surf.

That is why a height-only alert can be misleading. Pairing height with period helps avoid notifications triggered only by short-period wind chop.

Practical takeaway

For surf, do not read total wave height alone. Identify which component has the period and direction your coast can use.