Surf guide

How to read swell period, height and direction

SwellOracle is built around three simple signals: height, period and direction. None of them tells the whole story alone. The useful part is how they combine with local exposure, tide, wind and bathymetry.

Height is energy, not a guarantee

Wave height tells you how much surface motion is present at the measurement point. A buoy reading of 4 ft offshore can become a much larger breaking wave on an exposed reef, or fade into something modest inside a protected bay.

For alerts, height is a useful first filter. It should be paired with period so short local wind chop does not look like a proper groundswell.

Period separates swell from noise

Longer period waves usually carry more organized energy and can wrap farther around headlands. A 3 ft swell at 16 seconds can matter more than a 5 ft wind sea at 6 seconds.

As a rule of thumb, under 8 seconds often feels local and messy, 10 to 13 seconds can be workable, and 14 seconds or more often indicates stronger groundswell. Local coast shape still decides what reaches the beach.

Direction decides who receives the swell

Direction is the path the swell travels from. A southwest swell can light up a very different set of beaches than a west or northwest swell.

SwellOracle stores direction with each buoy or model point so alerts can be interpreted in context rather than treated as generic ocean energy.

Practical takeaway

Use height to filter size, period to filter quality, and direction to decide whether the swell can reach the coast you care about.