Glossary of surfing and marine weather
- Bathymetry
- Measurement of seabed depth. The seabed decides how the swell grows and breaks.
- Beach break
- A wave breaking over sand. Sandbanks move with storms: the spot changes from season to season.
- Breaking height
- Estimated size of the wave when it breaks near shore, different from the offshore swell. Isobath estimates it from the swell, its period and the beach orientation.
- Confidence
- How sure the forecast is: it drops with lead time and when models disagree. Never a guarantee.
- Cross-shore wind
- Wind parallel to the beach. Depending on strength, it can stay surfable or spoil the waves.
- Crossed swells
- Two swells arriving at the same time from different directions: waves get messier, with peaks that keep shifting. Isobath flags it when a second swell reaches at least 40% of the first with at least 40° between them.
- Ensemble forecast
- The same model run dozens of times with small differences at the start. The spread between scenarios shows how uncertain the future is.
- Forecast model
- A computer simulation of the atmosphere and ocean (Météo-France, ECMWF, NOAA…). Isobath crosses several to measure how much they agree.
- Gusts
- Peaks of wind above the average wind. Important for wind sports and for safety.
- Iribarren (breaker type)
- A number comparing the seabed slope with the wave steepness. Low: the wave spills gently into foam (gently sloping beach, ideal for beginners). Medium: it plunges and gets hollow. High: it surges and crashes on the shore (shorebreak).
- Offshore wind
- Wind blowing from land to sea. It holds up and smooths the waves: often the best conditions.
- Onshore wind
- Wind blowing from the sea onto the beach. It flattens the waves and makes the water messy.
- Peak period
- Period of the most energetic waves. Always a little longer than the mean period; Isobath converts everything to mean period to compare models.
- Period
- Time in seconds between two waves. The longer it is, the more energy the swell carries: at equal height, 14 s pushes much harder than 8 s.
- Persistence
- A naive forecast: “it will stay as it is now”. Used as a reference: a useful model must do better.
- Point break
- A wave peeling along a headland or cape, often long and in one direction.
- Range
- A “from … to …” interval rather than a single number: it honestly shows the forecast uncertainty.
- Reef
- A wave breaking over rock or coral. More consistent, but more dangerous if you fall.
- Rip currents
- Channels in the sand where water flows back out to sea. Do not swim against them: drift, then return to shore from the side.
- Seabed relief (EMODnet)
- The shape of the seabed in front of a spot, from the European EMODnet Bathymetry surveys. Isobath uses it to draw the seabed profile and estimate where the wave breaks. Resolution of about a hundred metres: shifting sandbanks do not show.
- Set
- A group of bigger waves arriving after a lull. Between sets, the water can look calm.
- Shorebreak
- A wave breaking violently very close to shore, in shallow water. Dangerous for neck and back.
- Submarine canyon
- A deep valley under the sea, like the Gouf de Capbreton. It focuses the swell on certain beaches, which get bigger waves.
- Swell
- Waves born far away under a storm that have travelled to the coast. They arrive lined up and regular: that is what we surf.
- Swell direction
- Where the swell comes from (degrees or compass points). A swell hitting the beach head-on gives more size than a grazing one.
- Tidal range
- Difference in water height between high and low tide.
- Tide
- Rise and fall of the sea level, about twice a day. Each spot works best at a certain stage of the tide.
- Tide coefficient
- A number from 20 to 120 giving the size of the tide (defined at Brest). Above 95, big spring tides: stronger currents, beaches covered at high tide.
- Wind sea
- Short waves raised by the local wind. They make the water choppy and messy.