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Surf Swell Glossary: Buoys, Period, Direction and Wind
Use this glossary to translate common swell and buoy terms into practical questions you can ask before planning a surf session.
Buoy
A buoy is a floating instrument or station that can measure ocean and weather conditions at its location. Depending on the provider, it may report waves, period, direction, wind, water temperature or only some of those variables.
A buoy reading describes conditions at the instrument, not the exact wave size at every beach nearby.
Swell height
Swell or wave height describes the size of offshore wave energy measured or estimated at a point. It is not automatically the height of breaking waves at a surf spot.
Read height with period, direction and local exposure before translating it into surf expectations.
Wave period
Period is the time in seconds between consecutive wave crests. Longer-period energy is generally spaced farther apart and can behave differently as it reaches reefs, points and bays.
A long period is not automatically better or safer. Direction, wind, tide, coastline shape and local knowledge still matter.
Swell direction
Direction indicates where offshore wave energy comes from. It is often reported as a compass direction or degrees, such as 270° for west.
The useful question is whether that angle reaches your coastline or is blocked, filtered or refracted by land and bathymetry.
Wind sea and groundswell
Wind sea is shorter-period wave energy generated by local or nearby wind. Groundswell usually refers to more organized energy that has traveled from a distant storm.
The sea state can contain both at once. A single height value may hide that mixture, which is why period and direction matter.
Marine model
A marine model estimates conditions for a geographic grid point. It is useful for coverage where no physical buoy is available, but it is not an instrument reading from the water.
Keep model estimates and observed data labelled separately when comparing them.
Practical takeaway
A surf forecast becomes more useful when you understand each term and read the variables together rather than in isolation.