How to read a surf forecast: a beginner's guide

Most forecasts show two heights, and they don't mean the same thing.

• Swell height: what the model calculates offshore, out in open water.
• Wave height (breaking height): what you'll actually paddle into, after the swell has met the seabed and the coastline.

Between the two sit the shape of the bottom and the orientation of the beach. A one-metre swell offshore can turn into 30 cm inside a sheltered bay and a solid metre and a half on a west-facing beach — same day, ten kilometres apart.

Then there's the trap that catches every beginner: the number you see is a significant wave height, meaning the average of the biggest third of the waves. In plain terms, the sea is not 1 m everywhere all the time. Plenty of waves are smaller, and the sets rolling through every few minutes can run roughly one and a half times the forecast. A "1 m" day contains 1.5 m waves — usually arriving exactly as you try to paddle out.

Period, in seconds, is the time between two waves passing the same point. It tells you more about the quality of the swell than the height does.

• 4 to 7 s: not really swell at all — local wind chop. Weak, disorganised, shapeless.
• 8 to 11 s: decent swell, and often the best compromise while you're learning.
• 12 to 15 s: proper groundswell, born from a distant storm. Organised, clean sets, powerful.
• 16 s and up: swell that has crossed an ocean. It breaks further out, steeper, and hits far harder than the height number suggests.

Why? A long-period swell travels fast, arrives in tidy groups and carries far more energy than chop of the same height. It also feels the seabed sooner, so it stands up further from shore. The rule that saves sessions: 1 m at 14 s and 1 m at 6 s are two different oceans. The first is a real surfable wave, the second is a washing machine.

The safety corollary is the part people miss: as a beginner, small height plus very long period is not "easy". The wave is faster, it jacks up suddenly, and the water pulling back out is stronger.

Both are given in degrees or compass points, and in both cases the number tells you where it comes FROM, never where it's going. 270° is due west; 315° is northwest.

Swell direction decides whether the wave reaches you at all. Every spot has a window: a headland, an island, a point, or simply the way the beach faces will block part of the compass. A west-facing beach loves a west–northwest swell and can sit flat under a south swell, however huge it looks offshore. Check this first — if the direction doesn't get in, nothing else matters.

Wind decides the state of the surface, and it's usually what settles the day.

• Offshore (blowing from land to sea): smooths the water and holds the wave face up. This is the wind in the pretty photos. Too strong and it makes the take-off hard.
• Onshore (sea to land): chops it up, kills the shape, leaves the wave soft and lumpy.
• Cross-shore (parallel to the beach): somewhere in between, depending on the spot.

Under 10 km/h the direction barely matters — it's close to glassy. Read the gusts, not just the average, and check your units (1 knot ≈ 1.85 km/h). Finally, remember the sea-breeze cycle: on sunny days the thermal wind tends to kick in late morning and build through the afternoon. That's the entire reason dawn patrol exists.

On Atlantic coasts the tide reshapes a spot within hours: it moves where the wave breaks and covers or exposes sandbars and rocks. Plenty of beach breaks only work around mid-tide; some reefs need enough water over them to be surfable at all. In the Mediterranean the range is so small you can ignore it. In France, also check the tidal coefficient (a 20–120 scale): above 100 the water moves fast and the currents get noticeably stronger.

The reading order that works, as four questions:

• 1. Direction: does the swell get into this spot? If not, drive to another beach.
• 2. Period and height together: what kind of wave is it, and is it my size?
• 3. Wind: will it be clean or blown out? A strong onshore ruins a day that looked perfect on paper.
• 4. Tide: which hours does this spot actually work?

The right session is where all four overlap — often a two-hour window, not the whole day. That overlap is exactly what Yosurf's level-based score compresses into a single number.

And then there's what no model displays: current, crowd and how you feel today. On the open beaches of southwest France, baïnes — troughs between sandbars — create rip currents that pull straight out to sea, especially around low tide and on big coefficients. If one grabs you, never paddle against it: move parallel to the beach, raise an arm, and stay near a lifeguarded zone. Add shore break on steep beaches, and the rule that outranks all the others: don't paddle out above your level just because the forecast looks good.