How to Read a Surf Forecast

A surf forecast is a list of numbers: swell height, period, direction, wind, tide and, more and more often, wave energy. On their own they are just weather data. Together they tell you whether your spot will be flat, perfect or dangerous, and at which hour.

1. Swell height

Swell is wave energy made by a storm far away. It travels across the ocean in orderly lines and arrives at the coast as the sets you surf. Forecasts give its height in metres or feet as significant wave height: the average height of the highest third of the waves in open water. Some sets will be bigger than the number, and many waves will be smaller.

Most forecasts list several swells at once, such as a primary swell and a secondary one. They can come from different storms and directions. A forecast that shows "wave" or "total sea" next to "swell" is adding the local wind chop to the clean swell.

2. Period: the number most people skip

Period is the time in seconds between two waves passing the same point. It tells you how much energy is hidden under the surface. A 1.5 m swell at 14 seconds is a completely different day from a 1.5 m swell at 7 seconds: the long-period swell arrives in clean, powerful sets that grow as they reach the reef or sandbank, while the short-period one is weak, close together and often messy. Read Swell Period Explained for the full picture.

3. Swell direction

Direction is where the swell comes from, written as a compass point or in degrees (a 270° swell comes from the west). Every spot has a swell window, the range of directions it is open to. A big swell from the wrong angle can leave a sheltered beach almost flat, while a small swell from the perfect angle can make it the best wave on the coast. Long-period swells bend (refract) more around headlands, so they reach spots a short-period swell from the same direction would miss.

4. Wind: speed and direction

Wind is what turns a good swell into a good or a bad session. It is also given as the direction it blows from. What matters is that direction relative to your beach:

• Offshore (land to sea): holds the wave face up, cleaner and hollower waves.
• Onshore (sea to land): pushes the waves over early, choppy and crumbly.
• Cross-shore (along the beach): somewhere in between, with a drift along the beach.

Below about 5 knots any direction is usually fine; this is the "glassy" surface you see at dawn. Above 12–15 knots onshore, most beach breaks are blown out. See Offshore, Onshore and Cross-shore Wind for how each one shapes the wave.

5. Tide

Tide changes the water depth over the sandbank or reef, and with it the shape of the wave. Some spots only work at low tide, some at mid tide on the push (rising), some only on the high. A big tidal range, such as a spring tide, changes a spot faster during the session. Learn your spots' tide windows: it is local knowledge no global forecast can give you. How Tides Work explains why we get two tides a day and how the Moon and the Sun change their size.

6. Wave energy

Many forecasts now combine height and period into a single energynumber, often in kilojoules (kJ). Because energy grows with the square of the height and in step with the period, it is a better guide to the real power of a swell than height alone. Wave Energy in Surf Forecasts explains the maths and the ranges that suit each level.

Putting it together: a worked example

Imagine a west-facing beach break and this forecast for tomorrow:

The swell is the same all day: a medium groundswell from a direction the beach is open to. The wind makes the difference. At 07:00 there is light offshore wind and a rising tide, the best session of the day. By 13:00 the sea breeze has turned onshore and the tide is full, so the waves will be soft and choppy. The evening may clean up a little, but cross-onshore wind rarely gives the quality of the morning. The plan: train at dawn.

Checking conditions in your training

When you create a training in Prosurfingtools and set its location, the training page shows the conditions for that spot: wind speed and direction, wave and swell height with their period, wave energy in kJ, air and water temperature and a tide curve around the current time. Each finished heat keeps a snapshot of the conditions it was surfed in, so you can look back at scores alongside the wind, swell and tide of the day and see which conditions each surfer performs best in.

Related guides

Swell Period ExplainedOffshore, Onshore and Cross-shore WindWave Energy in Surf ForecastsHow Tides Work