Marine guide
Marine weather explained
Marine weather is a specialized vocabulary — sea states, buoy reports, coastal warnings, small craft advisories. Here is how to read it if you are on the water or planning to be.
Reading a buoy report
NOAA buoys report every 10 minutes to ndbc.noaa.gov. A typical report:
- Wind — direction and speed at 10 meters above the deck
- Gust — peak instantaneous wind
- WVHT — significant wave height (average of highest 1/3)
- DPD — dominant wave period in seconds
- APD — average wave period
- MWD — mean wave direction
- PRES — barometric pressure at sea level
- ATMP — air temperature
- WTMP — water temperature
Sea states — the Douglas scale
- 0 — Calm. Sea surface glassy.
- 1 — Rippled. Wavelets under 4 inches.
- 2 — Smooth. Wavelets 4 in to 1.5 ft.
- 3 — Slight. Small waves 1.5-4 ft.
- 4 — Moderate. Moderate waves 4-8 ft.
- 5 — Rough. Large waves 8-13 ft, whitecaps.
- 6 — Very rough. High waves 13-20 ft.
- 7 — High. Very high 20-30 ft.
- 8 — Very high. Exceptionally high 30-45 ft.
- 9 — Phenomenal. Over 45 ft. Rare.
Warning categories
Small Craft Advisory
Winds 20-33 kt or waves ≥5 ft. Dangerous for small vessels.
Gale Warning
Winds 34-47 kt. Beyond most recreational vessels.
Storm Warning
Winds 48-63 kt. Damaging waves.
Hurricane Force Warning
Winds ≥64 kt. Tropical or extratropical.
Special Marine Warning
For short-lived hazards — waterspouts, sudden squalls, dangerous thunderstorms.
Coastal marine forecast structure
NWS coastal forecasts follow a pattern: general synopsis, then broken down by zone with wind, seas, weather, and visibility for tonight, tomorrow morning, tomorrow afternoon, etc.
Watch for the phrase "seas subsiding" (waves decreasing) vs "seas building" (waves increasing).
Where to check
- weather.gov/marine — official coastal forecasts
- ndbc.noaa.gov — buoy data
- nhc.noaa.gov — tropical weather
- sailflow.com — sailor-focused
- Windy Marine layer — visualization