Forecast models are smart but they're forecasts — predictions. Buoys are real, in the ocean, measuring waves and wind every 30 minutes. When forecasts disagree with what's actually happening, the buoy is usually right. Learning to read a buoy report is one of the highest-leverage skills a surfer can develop.
The two buoy networks
NDBC (National Data Buoy Center, NOAA) operates roughly 100 moored wave/weather buoys along US coasts and offshore. They measure wave height, peak period, dominant direction, wind speed/direction/gust, air and water temperature, and barometric pressure. Most are offshore — 20–250 nm from the coast.
CDIP (Coastal Data Information Program, Scripps) runs a network of nearshore wave buoys, mostly on the West Coast and Pacific. CDIP buoys are typically 10–20 nm offshore and produce higher-resolution directional wave spectra than NDBC — they tell you not just "5 ft at 12 s from the WNW" but the full distribution of energy across periods and directions.
The four numbers
Every buoy reports these:
- WVHT (wave height): significant wave height in meters or feet. The average of the largest 1/3 of waves.
- DPD (dominant period): peak period in seconds. The period carrying the most energy.
- APD (average period): mean period across all frequencies. Usually 1–2 s shorter than DPD.
- MWD (mean wave direction): dominant direction the waves are coming FROM, in degrees true. 90 = from east.
Plus wind: WSPD (speed, m/s), WDIR (direction from), GST (gust speed). And environmental: WTMP (water temp), ATMP (air temp), PRES (barometric pressure mb).
Translating offshore to beach
A buoy reads open-ocean conditions; you ride waves at the beach. The two can differ substantially:
- Offshore height > beach face height — usually. Once a swell crosses the continental shelf, shoaling can amplify height, but refraction loss and the angle between swell and beach orientation usually reduce face height vs offshore Hs.
- Period is preserved — mostly. Period doesn't change much from offshore to beach. The 14 s the buoy reports is essentially the 14 s you'll feel.
- Direction bends. Refraction turns swell direction toward shore-normal as it crosses the shelf. A 90° offshore direction may arrive at the beach as 75–80°.
For a typical East Coast beach with a relatively narrow shelf, beach face heights are often 30–50% smaller than offshore Hs from a deep-water buoy. A 3 ft buoy reading at 12 s might translate to 4 ft face heights on the bigger sets — but on an offshore reef buoy 100 nm out, the 3 ft might mean barely 1.5 ft at the beach. Distance from the coastline matters a lot.
Picking the right buoy
The buoy panel on every forecast page picks the closest stations and lists their distance. The closer the buoy, the more directly its readings apply. When the only available buoy is 150+ nm offshore, this site shows a warning — those readings are open-ocean and overstate beach heights significantly.
Look for buoys within 50 nm if you can. Within 20 nm is ideal. CDIP nearshore buoys (often within 5 nm) are gold for West Coast surfers.
The wave spectrum
The 1D spectrum chart on the buoy panel shows wave energy across frequencies. Useful patterns to recognize:
- A single sharp peak at long period (low frequency) = one organized ground swell. Clean conditions.
- Two or more peaks = mixed seas. Multiple swell trains. Lined-up sets interrupted by random chop.
- A broad peak at short period (high frequency) = local wind sea. Choppy, disorganized.
- The 2D directional spectrum (CDIP only) adds direction-of-arrival per frequency. A real luxury when available.
Buoys vs models, when they disagree
The buoy is measuring what's actually there. The model is predicting what it thinks should be there. When they disagree by more than ~25%, trust the buoy for the immediate window and treat the next 24 h of forecast with skepticism. Persistent model bias against buoy observations is what professional surf forecasters spend their careers correcting.
Practical use
- Check your nearest buoy before any session — it's the ground truth for the moment.
- Compare buoy readings to what the forecast said for that hour. If they're close, the forecast is probably reliable for the next day or so. If they're way off, weight the buoy more.
- For "should I go now" decisions, the buoy beats any forecast.
- For "should I drive 90 minutes tomorrow," the forecast is your only option — but knowing the current bias from buoy comparison helps calibrate it.