Marine Glossary

Breakers -

Waves that break, displaying white water. Depends on wave steepness and bottom bathymetry.

Combined Seas -

Combination of both wind waves and swell. Also called Seas.

Heavy Surf Advisory -

From Pt St George to Pt Arena, combined seas 18 feet or greater, a significant part of which is due to swell. North of Pt St George, combined seas 20 feet or greater. South of Pt Arena, combined seas 15 feet or greater.

Gale Warning -

Wind of 34 knots to 47 knots sustained or frequent gusts.

Group Velocity -

The speed at which a particular wave front or swell train advances.

Seas -

Waves generated by the action of wind blowing at the time of observation or in the recent past. Seas become swell at some point.

Significant Wave Height -

The mean or average height of the highest one third of all waves in a swell train or in a wave generating region. It also approximates the value an experienced observer would report if visually estimating sea height.

Small Craft Advisory -

Wind of 21 knots to 33 knots sustained or frequent gusts.

Small Craft Advisory for Hazardous Seas or for Swell -

Combined seas of 10 feet or greater.

Storm Warning -

Wind of 48 knots or greater.

Swell -

Wind waves which have traveled beyond the wave generation region.

Wave Height -

Distance from wave trough to wave crest.

Wave Period -

Time, in seconds for the passage of successive wave crests.

Wave Steepness -

Ratio of wave height to wavelength. Theoretical wave steepness maximum is around 1/10, after which the wave becomes unstable and breaks.

Wave Trough -

The lowest part of the wave.

Whitecap -

The breaking crest of a wave, usually white and frothy.

Wind Waves -

Waves generated locally by wind blowing at the time of observation.

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