Understanding Buoy Data

Buoy data is essential for understanding ocean conditions and forecasting surf. Here's what each measurement means and how to use it.

Wave Height

Wave height is the average height of the largest waves measured over a 20-minute window — specifically, the top one-third of all waves recorded. It represents what an experienced observer would call the "average" wave height. Individual waves can run significantly larger than this number, sometimes twice as high.

This is your broadest indicator of wave size. It captures all energy on the water surface — organized swell, local wind chop, and anything else happening at that moment — combined into a single number.

Swell Height

Swell height measures only the organized, long-period energy traveling from a distant storm. Unlike wave height, it filters out the local wind chop and short-period disturbances that clutter the surface reading.

This number tells you how much of the ocean's energy is actually useful swell versus surface noise.

Wave Height vs. Swell Height — When these two numbers are close together, conditions are likely clean and organized. When there's a significant gap, a lot of that wave height is disorganized chop rather than real swell. A reading of 6ft wave height with 3ft swell height means roughly half that energy is surface mess — the day will feel smaller and choppier than the wave height alone suggests.

Wind Wave Height

Wind wave height is the portion of wave height generated by local winds at or near the buoy. It's the complement to swell height — together they make up the total wave height reading.

High wind wave height relative to swell height usually means messy, choppy conditions. When wind wave height is low and swell height is carrying most of the total, the surf tends to be cleaner and better-organized.

Swell Period

Swell period is the time in seconds between successive swell crests passing the buoy. It's one of the most important numbers for understanding wave quality.

• Under 8 seconds — short-period wind swell, typically choppy and weak
• 8–12 seconds — moderate swell, reasonable surf in most conditions
• 12+ seconds — ground swell from a distant storm, powerful and well-organized

Longer periods mean the swell has traveled farther and carries more energy per wave. A 4ft reading at 16 seconds will break with significantly more power than the same height at 8 seconds.

Wind Wave Period

Wind wave period is the time between crests of the locally-generated wind waves. These are almost always shorter than swell periods since they haven't had the distance to organize and lengthen.

Reading this alongside swell period helps you understand the mix of energy in the water. A large gap between swell period and wind wave period — say 15 seconds vs. 6 seconds — suggests a well-defined ground swell arriving on top of choppy local surface conditions.

Wave Direction

Wave direction is the compass bearing the waves are arriving from, measured in degrees. 0° is north, 90° is east, 180° is south, 270° is west.

Direction determines which spots will light up for a given swell. A west swell at 270° will wrap into west-facing breaks while leaving east-facing beaches sheltered. Knowing your local break's optimal swell window makes this number immediately actionable.

Putting It Together

A useful buoy reading tells a story, not just a size. A session with 5ft wave height, 4.5ft swell height, a 14-second swell period, and a 280° direction is a very different day than 5ft wave height with 2ft swell height, an 8-second period, and a mixed direction — even though both show the same wave height. The period and the gap between wave and swell height are often what separates a good session from a forgettable one.

For a deeper technical reference on how NOAA defines each measurement, see the NDBC measurement descriptions from the National Data Buoy Center.