Before every session, there’s a ritual: open the app and scan the numbers. But there’s a world between « looking at the forecast » and « knowing how to read it » — and when you switch to foiling, the parameters that matter change again. Here’s how to decode a surf forecast.
Swell: far more than just height
Most people look at the height and stop there. That’s the classic mistake. A swell reads across several data points:
- Height — the size of the waves offshore. The most-watched, the least meaningful on its own.
- Period — the time, in seconds, between two wave trains. The key number. Short (under 8 s) = wind swell, messy and soft. Long (12 s and up) = ground swell born far offshore: powerful, organised, peeling. Two 1 m swells have nothing in common if one is at 6 s and the other at 14 s.
- Direction — where the swell comes from. Depending on how the spot faces, the same swell can deliver everything… or never come in.
- Swell energy — the metric on the rise, in kJ/m². It combines height and period into one value and reflects the real power reaching the coast. At equal height, two swells of different periods carry very different energy — often a far better indicator than height alone of whether « it’ll push ».
Wind: what makes or breaks the session
Two things matter: its strength and its direction.
- Offshore (land to sea): smooths the surface, hollows the waves, holds them. The ideal wind — a whisper of offshore transforms a session.
- Onshore (sea to land): chops the surface, softens everything. Too much onshore and the waves turn shapeless.
- Cross-shore (sideways): in between, depending on the spot’s orientation and the strength.
A light, well-oriented wind (5 to 10 knots) is perfect; beyond 15 to 20 knots of onshore, most spots close out. Wind shifts through the day: the calmer morning windows are precious.
Tide: the parameter everyone forgets
Many spots only work at a certain tide, or a precise window. The same spot can be perfect at mid rising tide and unrideable two hours later. Tide changes the depth, and therefore how the wave breaks on the bottom. Check the tide coefficient and times for your spot.
Ratings aren’t an absolute truth
Classic trap: blindly trusting the rating (stars, a score out of 10) shown by the sites. These ratings are largely subjective, and above all calibrated for an experienced surfer after powerful, well-formed waves. Surfline’s, Windguru’s or surf-forecast’s « good » isn’t necessarily yours.
A beginner will have a blast in small mushy waves rated « poor ». A foiler will find gold in 50 cm that every site calls « flat ». Learn to read the raw data rather than the rating, and build your own scale — based on your level, your gear and what you enjoy.
What foiling changes
In foiling, reading the forecast takes on another dimension. Three parameters become critical:
- Wind, differently. You ride far smaller, softer conditions than in surfing: a 50 cm swell becomes rideable. So you chase light-wind windows and the small swells surfers ignore. In wingfoiling it’s the opposite: wind is exactly what you want.
- Water depth. The parameter unique to foiling: a mast and wings reach down 70–90 cm. Too little water — low tide, a rising bottom, a sandbar — and the foil hits the bottom: gear damage and a violent fall. Check the depth at the relevant tide.
- Currents. You drift from the peak, pump, cover ground. A current pushing out to sea or toward the rocks is something to anticipate before you paddle out.
The tools: data, ratings… and webcams
For swell, wind and tide, each service has its strengths:
- Windguru — the data reference, dense and reliable.
- Windy — the animated map, perfect for visualising wind and fronts.
- Surfline — strong on premium spots, expert forecasts and plenty of webcams.
- surf-forecast — handy for a spot-by-spot read.
And don’t forget webcams: many spots have one, freely accessible. Nothing beats a live look at the real state of the sea before you load the car — data predicts, the webcam confirms.
For foiling, these tools don’t cross-reference everything (swell, wind, tide, depth) from a foiler’s point of view: a foil-focused resource like foil-viewer.ovh helps you spot the right windows.
A concrete example: Hendaye vs Seignosse
Take two neighbouring spots and the same data: a swell energy of around 1200–1500 kJ/m².
At Hendaye, a bay sheltered at the bottom of the coast, that energy gives accessible conditions: the swell arrives filtered, the bay takes the edge off it. The result — easily surfable and foilable, even at a beginner-to-intermediate level.
At Seignosse, an exposed beach break facing the open ocean, the same energy is a whole other story: the swell hits unfiltered, the sets are powerful, the currents strong. At 1200–1500 kJ, the spot is reserved for experienced surfers.
Same number, two opposite realities. That’s exactly why a universal rating means nothing — and why knowing your spot’s personality is worth more than any forecast.
The real secret: study your spot
No forecast replaces knowing a spot. The data describes what arrives offshore; your spot turns that data into real waves, depending on its bottom, its sandbars and its exposure — the Hendaye / Seignosse example shows it well. The only real way to understand a spot and find your best windows is to study it, session after session:
- Tides — at what tide it opens and closes.
- Currents (rips) — where it pulls, where it creates channels. Useful for paddling smart, essential for your safety.
- Wave formation — how the swell wakes up on a given sandbar or shoal, where the peak forms and how it shifts with size and direction.
Sandbars move, the bottom changes: a spot is never fixed. Keeping a session journal — the day’s conditions (swell, period, energy, wind, tide) and what it actually delivered — is one of the most effective ways to build that knowledge. Tools like foil-viewer.ovh also help you keep track of your sessions and cross-reference conditions with how it felt. Over time, you read your spot better than any app.
Reading a forecast well is already half of a good session. The rest is knowing your spot and being ready once you’re in the water — with the right gear, to stay focused on what matters: the ride.