Third image, ‘Kylie’ a trawler built by Adelaide Ship Construction International.
Marine weather services
The Bureau of Meteorology provides the Australian and international maritime communities with weather forecasts, warnings and observations for coastal waters areas and high seas around Australia (under the Safety of Life at Sea convention). Generally most of these services are provided routinely throughout the day, while marine weather warnings may be issued at any time when the need becomes apparent.
The marine forecasts include wind, weather, sea and swell and are intended to describe the average conditions over specified areas.
Marine weather warnings
Warnings for coastal waters are issued whenever strong winds, gales, storm force or hurricane force winds are expected. The initial warning attempts to provide around 24 hours lead-time and warnings are renewed every 6 hours.
Warnings to shipping on the high seas are issued whenever gale, storm force or hurricane force winds are expected. The initial warning attempts to provide around 24 hours lead-time and warnings are renewed every 6 hours.
Coastal waters forecasts are for areas within 60 nautical miles of the coast (see map for coastal waters areas). Coastal waters and local waters forecasts are issued twice daily and monitored continuously for changes which may occur. Updates may be issued at other times.
High seas forecasts are issued twice daily for the areas beyond the coastal waters surrounding Australia.
Forecasts of winds
The Bureau forecasts of wind speed and direction are average (or mean) values over a 10 minute period at a height of 10 metres. Wind speeds usually increase with height above the sea-surface. When there are expected variations along a coastal area a range may be given, for example 15 to 25 knots.
Forecasts of gusts are not included as routine, however statistically it is estimated that gusts typically exceed the average wind speed by about one third. For example, if the forecast (average) wind speed is 15 knots, and one third of 15 is 5, gusts of around 20 knots can be expected. Gusts are generally associated with showers, thunderstorms and fronts.
Figure 1 Wind trace from an anemograph. This shows a recording of instantaneous wind speed. The dark blue trace illustrates the variability (gustiness) of wind speed. The higher wind speeds are typically one-third above the average. Squalls are also evident. These may have occurred as showers or thunderstorms passed over the recording site.
Sea and swell forecasts
Forecasts of sea and swell in coastal waters forecasts are given in metres and describe the height, which is the average height of the highest one-third of the waves (see definitions and terminology).
Some waves will be higher and some lower than the forecast and observed height.
The Bureau of Meteorology does not forecast maximum wave heights in routine forecasts.
Statistically it is estimated that about one in every 2000 to 3000 waves (three to four times a day) will be approximately twice the height of the significant wave. Forecasts for high seas describe sea and swell using terms such as slight, moderate, rough etc. in place of wave heights in metres.
Figure 2 Significant and Maximum wave heights at Cape Sorell, west coast of Tasmania. The recording illustrates that maximum wave heights can be twice the significant wave height. It shows a maximum wave height of two and a half times the significant wave height (4am, 3 April 2004). This is sometimes referred to as a Rogue or King wave.
The Bureau's coastal waters forecast have traditionally focused on the larger primary swell. However, recent improvements in wave observations and computer wave models have enabled the Bureau to include the second swell in the forecast if relevant.
Find more information, view our Second Swell page.
Marine weather observations
Latest coastal weather observations for states and territories show the most currently reported weather conditions at weather stations near or on the coast. Some stations also include sea and swell information.
Marine services for offshore yacht races
Every day, the Bureau of Meteorology's routine marine and ocean service provides critical wind, wave and ocean information that will assist racing yachts plan for a safe journey.
Bureau Oceanographic services include tide prediction, tsunami warnings and ocean forecasts including sea surface temperature, sea surface salinity, currents and sea level anomaly via the BLUElink ocean forecasting project. These are linked below the Marine menu.
General weather services
In addition to specific marine weather information, other general weather information is relevant to mariners. A selection of general weather services are linked from the marine website.
Definitions and terminology
Beaufort wind scale: uses observations of
the effects of wind to estimate its speed.
Beaufort Wind Scale
Wind speed is the average speed of the wind over a 10-minute period at a height of 10 metres above the surface. As a guide, double the wind speed in knots to convert to kilometres per hour; for example 20 knots is approximately 40 km/h.
Gusts are increases in wind speed lasting for just a few seconds. The speeds are typically 30 to 40 per cent higher than the average wind speed, but stronger gusts are likely in the vicinity of showers, thunderstorms and frontal systems.
A squall is an abrupt and large increase in wind speed that usually only lasts for minutes then diminishes rather suddenly.
Strong wind warning: 26 to 33 knots.
Gale warning: 34 to 47 knots.
Storm force wind warning: 48 to 63 knots.
Hurricane force wind warning: 64 knots or more.
Wind direction is given in 8 compass points for forecasts and 16 for observations and is the direction the wind is coming from.
Wind direction descriptions
Sea (or wind) waves are generated by the local prevailing wind and vary in size according to the length of time a particular wind has been blowing, the fetch (distance the wind has blown over the sea) and the water depth.
Swell waves are the regular longer period waves generated by distant weather systems. There may be several sets of swell waves travelling in different directions, causing a confused sea state.
Combined sea and swell is also known as total wave height, or significant wave height. Combined sea and swell describes the combined height of the sea and the swell that mariners experience on open waters. The height of the Combined sea and swell refers to the average wave height of the highest one third of the waves.
A lookup table has been developed to outline how to calculate the Combined sea and swell.
Sea state describes the combination of sea (wind) waves and swell.
Wave height (trough to crest) for both sea and swell refers to 'significant wave height' which represents the average height of the highest one-third of the waves. Some waves will be higher and some lower than the significant wave height. The probable maximum wave height can be up to twice the significant wave height.
King or rogue waves are waves typically greater than twice the significant wave height. These very large waves are known to occur in areas where ocean currents run opposite to the prevailing sea and swell and where waves overrun each other, generating steep and dangerous seas. Mariners should be prepared for a rogue wave encounter.
UTC (Coordinated Universal Time): time references in forecasts and warnings for high seas are given in UTC. Australian Eastern Standard Time is UTC+10 h. Central Standard Time is UTC+9.5 h. Western Standard Time is UTC+8 h.
Ways to get weather information
Please refer to Communications Services for information about how to access Bureau weather information at sea.