How to read a surf forecast: swell height, period, wind and tide explained

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A surf forecast packs a lot into a few numbers and arrows. Once you understand what each one means, you can tell the difference between a day that looks big on paper but turns out messy and a day with small, clean waves that are perfect for learning. Here is how to read the main parts.

Swell height

This is the height of the swell out in open water, usually in feet or metres. It is not the same as the size of the waves breaking on your beach. How big the waves get when they reach shore depends on the period, the direction of the swell and the shape of the seabed. Many forecasts also give an estimated surf height for a particular spot, which is more useful to a beginner.

Swell period

The period is the time in seconds between one wave crest and the next. It is one of the most important numbers on the forecast.

Short period (single digits) usually means wind swell, made by local winds. Waves are weaker, closer together and often choppy.
Long period (into the teens) usually means groundswell, generated by distant storms. Waves are more powerful, more organised and arrive in sets with lulls between.

A long-period swell carries more energy, so a modest swell height with a long period can break much bigger than the number suggests. For beginners, a small swell is safest; a big swell with a long period can be powerful and unpredictable.

Swell direction

The arrow shows where the swell is coming from. Every beach faces a certain way and is exposed to some directions and sheltered from others. Learning which directions work for your local beach is one of the most useful things you can pick up from experienced surfers.

Wind direction and strength

Wind changes the shape of the waves more than almost anything.

Offshore wind blows from the land towards the sea. In light to moderate strengths it grooms the waves, holding them up and making clean faces.
Onshore wind blows from the sea towards the land. It makes waves crumble, bumpy and messy.
Cross-shore wind blows along the beach and is somewhere in between.
No wind, or very light, often gives glassy water, especially early in the morning.

Strong offshore wind can make it hard to paddle into waves and can push you out. Strong onshore wind makes conditions choppy and tiring.

Tide

Many breaks work best at a particular stage of the tide. On some beaches waves dump hard on the sand at low tide; on others there are no waves at high tide because the water is too deep over the sandbank or reef. Forecasts show the times of high and low tide; local knowledge tells you which works at your spot. Currents can also be stronger as the tide moves.

Picking beginner-friendly days

For learning, look for:

Small surf, roughly knee to waist high at the spot
Light or offshore wind, or glassy early mornings
Moderate periods, so waves are not too powerful
A sheltered beach with a gently sloping sandy bottom
Lifeguarded beaches in season

Avoid days with large swell, strong onshore wind or warnings issued for your coast.

Reading it in practice

Check the forecast a day or two before, then again on the morning.
Compare it with what you see: watch the water for ten to fifteen minutes before paddling out.
Keep a short note of each session: swell, period, wind, tide and what it was actually like. After a few weeks you will see patterns for your own beach.
Remember forecasts are models. They are usually close, but not always.

What forecast details do you look at first, and which combination works best at your local beach? Share your tips and questions in the comments.