Reading Wave Data: The Three Core Metrics

When analyzing wave conditions via marine buoys or coastal forecasts, three metrics determine how that energy behaves when it hits the coast:

1. Significant Wave Height

This represents the average height of the highest one-third of all waves measured during a specific sampling period.

Note: Individual waves within a set can legally be up to twice the size of the reported significant wave height, especially when crossing shallow sandbars or reef shelves.

2. Wave Period (Interval)

Measured in seconds, this is the time it takes for two consecutive wave crests to pass a fixed point (like a buoy).

• Short Period (4–9 seconds): Local wind swell. The waves are close together, choppy, and carry less vertical energy.
• Long Period (12–20+ seconds): Deep-ocean ground swell. These waves travel deep beneath the surface. As they feel the ocean floor near the coast, they slow down, steepen, and grow significantly taller than their deep-water buoy height.

A Note on Southern California Swell Mechanics: A forecast showing a “3-foot wave height” can mean two completely different things for safety. A 3ft swell at 15 seconds indicates a powerful, deep-water groundswell filtering around the islands, whereas a 3ft wave at 5 seconds indicates short-period, steep wind-chop that makes for a miserable and potentially hazardous ride in smaller hulls. Always cross-reference the wave height with the dominant wave period.

3. Wave Direction (Degrees)

The angle from which the waves are arriving. Because the SoCal coastline twists and is heavily blocked by the Channel Islands (a phenomenon known as island shadowing), direction dictates exactly which beaches get hit and which stay completely flat.

• 180° – 210° (South/Southwest): Bypasses most island shadows to illuminate south-facing beaches (e.g., Malibu, Newport, San Clemente). Common in summer.
• 270° – 310° (West/Northwest): Direct energy for west-facing beaches (e.g., Manhattan Beach, Huntington, Carlsbad). Common in winter.

national weather service Coastal Wave Details Forecast for California
National Weather Service Los Angeles/Oxnard CA

national weather service Coastal Wave Details Forecast for California
National Weather Service San Diego CA

Tides -Los Angeles

Tides -San Diego