Reckoning / Weather / State of the sea
Weather · WMO code 3700
State of the sea
Observers on ships report the sea as one figure from 0 to 9. The heights are for well-developed wind waves in the open sea; the words come first and the heights are a guide.
| Code | Description | Height, m | |
|---|---|---|---|
| 0 | Calm (glassy) | 0 | |
| 1 | Calm (rippled) | 0–0.1 | |
| 2 | Smooth (wavelets) | 0.1–0.5 | |
| 3 | Slight | 0.5–1.25 | |
| 4 | Moderate | 1.25–2.5 | |
| 5 | Rough | 2.5–4 | |
| 6 | Very rough | 4–6 | |
| 7 | High | 6–9 | |
| 8 | Very high | 9–14 | |
| 9 | Phenomenal | over 14 |
Source: Manual on Codes, Volume I.1 (WMO-No. 306): code table 3700 (state of the sea) and 4677 (present weather). A height exactly on a boundary takes the lower code figure: 4 m is coded 5.
Sea and swell
Wind waves are raised by the wind blowing now; swell is wave energy that has travelled out of the area where it was raised, long and regular. A calm day can carry a heavy swell from a storm a thousand miles away.