Significant Wave Height

Abbreviation: Hs

Statistical measure of sea state: average height of the highest one-third of waves observed.

In practice

Forecast values from numerical models (ECMWF, GFS) underpin every weather routing decision. SWH > 5 m typically prompts speed reduction or route change.

Regulatory detail & full definition

The standard wave-height value reported in all marine forecasts (NOAA, ECMWF, Met Office). A few individual waves can be ~1.7× Hs (10% probability) or even ~2× Hs (rogue waves, ~1 in 3,000 waves). Used by routing software and stability assessments.

Authoritative source: WMO Sea State Code ↗

Source: WMO Sea State Code; IMO MSC.1/Circ.1228 (Operational guidance to masters in adverse weather)

High confidence

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Significant Wave Height

In practice

Related

Significant Wave Height

In practice

Related