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.
Wind
Direction
Indicates the direction from which the wind is blowing
Speed
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
Veering
The changing of the wind direction clockwise, e.g. SW to W
Backing
The changing of the wind in the opposite direction to veering (anticlockwise), e.g. SE to NE
Sea
Wave direction
The direction from which a wave propagates
Wind-Sea
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.
Hmax
Maximum wave height for specified period of time
Swell
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.
References:
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
