How to read a surf forecast (and actually trust it)

A surf forecast is just four numbers — wave height, period, direction and wind. Read them together and they tell you everything: how big it will be, how good it will be, and when to go. Read them wrong and you’ll show up to three-foot onshore closeouts thinking you scored.

Wave height: the size of the swell offshore

Forecast sites (including every page on SE Surf) report significant wave height in metres — the average of the tallest third of waves at sea. Two things matter here:

• Forecast height ≠ face height at the beach. A “1.5 m” forecast might be head-high at a beach break that doubles up, waist-high at a soft point, or ten feet at a reef like Nazaré that focuses energy. Every spot has its own multiplier. That’s why our spot pages pair the forecast with each break’s ideal size range.
• The trend matters more than the number. A building 1.2 m is getting fun; a dropping 1.2 m is dying. Check the hourly chart: you want to be in the water on the rise or at the peak, not after it.

Period: the quality dial

Wave period is the seconds between waves. It is the single best indicator of quality:

• Below 8 seconds — windswell, generated nearby. Messy, disorganised, closing out.
• 9–11 seconds — decent mid-range swell. Rideable, sometimes fun.
• 12–15 seconds — groundswell. Clean, powerful lines with a long energy spine.
• 16+ seconds — long-period groundswell. The waves that make seasons.

Long-period swells also wrap around headlands and focus on certain banks, which is why a 13-second swell can be tiny at one beach and perfect at the point two kilometres away. Short-period swell barely bends — it just marches straight in.

Direction: which windows matter

Swell direction is where a spot’s geography starts to matter. Every break has a swell window — the directions it can “see”. Pipeline works on north-west swells; Mundaka wants north-west too but from a very different angle; a south-facing beach might miss a north swell entirely.

On SE Surf each spot lists its best swell direction. Compare it with the forecast’s dominant direction (the arrow next to the wave height):

• Forecast direction inside the spot’s window → the size forecast is trustworthy.
• Direction at the edge of the window → expect less than the forecast says.
• Direction outside the window → the swell is missing you, whatever the size.

Wind: the difference between good and postcard

Wind is the easiest number to read and the most brutal. Wind is always labelled by the direction it blows from:

• Offshore (blowing from land to sea) — holds faces open, groomed, spitting barrels. Generally up to ~25 km/h is great; beyond that it’s hard to take off and get in.
• Cross-shore — chops the face but often keeps sections walled and open.
• Onshore (from sea to land) — closes out most waves and ruins most days. But note: an onshore morning often means clean evenings when it swings, and some spots only work because a local wind gap blows offshore in the afternoons.

That’s why our wind chart colours each bar green (offshore for that exact spot), blue (cross-shore) or red (onshore) — checked against the spot’s known offshore direction, not some generic number.

Putting it together: the 30-second check

1. Daily cards — pick the day with the best combination of size, period and green wind bars.
2. Wave chart — find the hours where height is in the spot’s ideal range and period is longest.
3. Wind chart — overlay: you want the morning before the sea breeze, or the evening wind switch.
4. Tide — check our tide panel; most spots have a two-to-three-hour window when the bank is working.
5. Rating — our 0–100 score crunches all of the above per hour. It’s a shortcut, not a gospel: use it to find the window, then trust your local knowledge.

The honest limits of forecasting

Models resolve the ocean on a grid of roughly 8–25 km. A forecast for “Ocean Beach” is an average over that cell — real waves vary sandbar by sandbar, tide by tide. Forecast skill is genuinely excellent at 3 days, decent at 5, and directional at 7. Use the long range to plan days off; use the 48-hour window to plan sessions.

The fastest way to learn is to compare: open a spot page, screenshot the forecast, and score yourself against reality at the end of the day.

Then close the laptop and go look at the water.