Surf Period Explained
Answer: Surf period is the number of seconds between consecutive wave crests passing a buoy. Short periods (under 10s) mean choppy, weak, locally-generated waves. Long periods (14s+) mean well-spaced, powerful, long-travelled swell that produces better surf. A forecast of 4ft @ 15s is typically a better session than 6ft @ 8s — the period is the stronger signal.
What period actually measures
NDBC buoys sit on the open ocean and record how long, in seconds, between one wave crest passing them and the next. That interval is the period. Physically, period is a proxy for how deep into the water column the wave’s energy extends — a 15-second wave moves energy hundreds of feet below the surface, while an 8-second wave barely moves the top of the water column.
Why it matters more than height
Wave energy scales roughly as the square of height and linearly with period. That means a small increase in period carries the same kick as a big increase in height. For surfers, this translates to:
- Long-period waves wrap around headlands and into bays better.
- They refract cleanly over reefs and points, lining up for shape.
- They’re spaced farther apart, so the lineup doesn’t get pounded.
- They carry more push on takeoff — easier to catch, more speed down the line.
The fields on a buoy report
- DPD (dominant wave period) — period of the strongest spectral peak. This is what most forecasts cite.
- APD (average wave period) — average of all waves in the spectrum; usually lower than DPD.
- WVHT (significant wave height) — average height of the top third of waves.
Most surfers read DPD first, WVHT second. A report like "3.2m @ 14s" from NDBC station 46042 (Monterey Bay) means a substantial mid-period groundswell is running.
How LazySurfer uses period
Period is one of seven parameters LazySurfer’s Similarity Score compares against your logged sessions (wave height, period, direction, wind speed, wind direction, tide height, tide direction). The on-device ML model learns the period range you tend to rate highly and weights forecasts accordingly.
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