Weather Forecast Glossary

This content aims to help users to read the relevant information within the right contextual data usage. The Weather information provided by Global MeteOcean or available through thescreenweather Web Portal follows International Standard Terminology and acronyms, commonly used by experts and users.



Indicates the direction from which the wind is blowing


The sustained wind speed over a given period at a given height above the sea surface (10 metres, 50metres or other heights) and associated direction, usually expressed as 10 minute mean – mean wind speed measured over 10 minutes.

Becoming cyclonic

Indicates that there will be considerable change in wind direction across the path of a depression within the forecast area


The changing of the wind direction clockwise, e.g. SW to W


The changing of the wind in the opposite direction to veering (anticlockwise), e.g. SE to NE


Wave direction

The direction from which a wave propagates


Component of the sea state related to locally generated wind.

Significant Wave Height (Hs)

Averaged wave height of the third largest crest to trough wave height.


Maximum wave height for specified period of time


Component of the sea state in which waves generated by wind remote from the site have traveled to the site rather than being locally generated.

Peak Period

The period corresponding to the frequency where the spectral density reaches its maximum.

Sea State

Condition of the sea during a period of time in which its statistics remain approximately stationary. In a statistical sense the sea state does not change significantly within the period. The time period during which this condition exists is generally 3 hours but it depends on the particular weather situation at any given time.

Visual Description of Sea State:

Smooth: Wave height less than 0.5 m

Slight: Wave height of 0.5 to 1.25 m

Moderate: Wave height of 1.25 to 2.5 m

Rough: Wave height of 2.5 to 4.0 m

Very rough: Wave height of 4.0 to 6.0 m

High: Wave height of 6.0 to 9.0 m

Very high: Wave height of 9.0 to 14.0 m

Phenomenal: Wave height more than 14.0 m

Wave crest elevation

The elevation of an individual wave crest above the still water level

Wave Spectrum

The wave spectrum or spectral density describes how the variance of the sea surface elevation is distributed over frequency and propagation direction, from which all wave parameters may be derived.


American Meteorological Society (AMS) Glossary of Meteorology

World Meteorological Organization (WMO) Weather Glossary

Met Office Marine Forecast Glossary

Guide to Wave Analysis and Forecasting (WMO)

IMarEST Metocean Procedures Guide for Offshore Renewables

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