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About WMO Code Table 3700

Code Table 3700: Sea State

Code Figure Descriptive terms Height* (in meters)
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
Notes:

(1) * These values refer to well-developed wind waves of the open sea. While priority shall be given to the descriptive terms, these height values may be used for guidance by the observer when reporting the total state of agitation of the sea resulting from various factors such as wind, swell, currents, angle between swell and wind, etc.

(2) The exact bounding height shall be assigned for the lower code figure; e.g. a height of 4 m is coded as 5.