How to Read Ocean Buoys: Tips & Resources

Ocean buoys are one of the greatest resources that surfers and mariners have at their disposal. The real-time wave observations reported by these buoys provide valuable insight into current ocean conditions, but they can be difficult to understand and interpret.

The reality is that reading ocean buoys is more of an art than a science. It requires a general understanding of basic wave theory concepts, but also requires a bit of experience and local knowledge. The following overview touches on the basics of wave theory, defines the data being reported by the buoys, and provides a few tips to get you started.

Understand the Basics of Wave Theory

Take the time to understand the science of waves, particularly how they are formed and their characteristics. One of the best overviews on the web is the Wind Wave article on Wikipedia. Read it. Seriously, go read it right now… we’ll wait.

Swell Height, Swell Period, and Swell Direction

Understanding swell height and swell period is critical, as it is arguably the most valuable data reported by ocean buoys. Here are their definitions, as provided by the National Data Buoy Center:

Swell height is the vertical distance between any swell crest and the succeeding swell wave trough. Swell period is the time (usually measured in seconds) that it takes successive swell wave crests or troughs to pass a fixed point.

The longer the swell period, the faster the swell travels. Long-period swells (swell period of 13 seconds or more) are often referred to as ground swells, and tend to have traveled farther and be more organized than short-period swells (swell period of 12 seconds or less).

The term long-period forerunners refers to a group of waves with a swell period of 20 seconds or more. Because of their long swell period, they travel faster than the rest of the waves and provide the first indications of an incoming swell.

As for swell direction, remember that it is the direction the swell is coming from. The units are degrees from true North, increasing clockwise, with North as 0° and East as 90°. For example, a pure West swell (270°) is coming from the West, but actually traveling East.

Significant Wave Height

Significant Wave Height Diagram

Significant wave height is a statistical representation of the height that a “trained observer” would report, and is calculated as the average of the highest one-third of all the wave heights during the sampling period. The important characteristic of this measurement is that it is sampled from all wave heights and may contain wave height data from any number of swell components, including those traveling in opposite directions.

Tip: Use Swell Data, Not Significant Wave Height

Buoys are individually equipped with different sensor packages, which means measurements vary per buoy. While nearly all stations report significant wave height, some also report air temperature, water temperature, wind, and pressure data. However, the buoys that report swell data are most valuable to surfers.

Why? Because swell reports provide height, period, and directional data for a single swell component, while significant wave height is the average of all wave heights, from all swell components. The latter is important for mariners, who venture into the open ocean and have to contend with the additive mixture of swells from all directions. But for surfers, the shoreline typically eliminates about 180° of the potential swell direction (East swell in California? No way.), and the reality is you can only catch one wave at a time.

There is an important caveat to swell reports: they are only representative of the dominant swell. This means that it is possible (and often probable) that additional swell components with less energy may also exist and fail to be reported. There are ways to account for this using additional data, but we’ll save that for another post.

Tip: Keep a Journal

This is where the art of buoy reading comes into play. By keeping a journal of your sessions, you can begin to correlate observed buoy reports to your own experiences in the water.

Every swell is unique, as is each surf break. Over time, the particular conditions that you prefer, or that a certain spot requires, will become clearer. As your knowledge and understand grows, you can begin to monitor the buoys for similar reports, and cross-reference them against your notes. Pretty soon you’ll be the person everyone is calling for the forecast.

Tip: The Buoys Are Only One Tool

Remember, the buoys are only one tool in your utility belt. Plenty of other factors that are not reported by the buoys also contribute to the quality of the surf. There are tons of resources available online, including weather forecasts, tide charts, and surf cams. Use them all.

Additional Resources & Further Reading

  1. How to Forecast the Surf: Lesson One Swell Profile
  2. Stormsurf: Wave Basics
  3. Surfline: Reading the Southern California Buoys with Sean Collins
  4. Surfer Magazine: How to Read the Buoys