Marine weather forecast services include:
- Local waters forecasts
- Coastal waters forecasts
- High seas forecasts
Local waters forecasts are for local waters such as bays, harbours and inland waters on which a large number of commercial and/or pleasure craft operate. Local waters forecasts are issued by Regional Forecasting Centres in each capital city generally twice daily and monitored continuously for changes which may occur. Updates may be issued at other times.
Coastal waters forecasts are for areas within 60 nautical miles of the coast (see map for coastal waters areas). Coastal waters forecasts are issued by Regional Forecasting Centres in each capital city generally twice daily and monitored continuously for changes which may occur. Updates may be issued at other times.
High seas forecasts are issued twice daily by the Regional Forecasting Centres in Perth, Darwin, Brisbane and Melbourne for the areas beyond the coastal waters surrounding Australia.
The Coastal Waters forecast is now an all-in-one product for warning and forecast information. Wind warning statements are inserted into the forecast for today or tomorrow. The details of wind strength, direction and timing are located directly below the wind warning statement. If a Coastal Waters zone is affected by a wind warning, the forecast will be updated every six-hours.
Example forecast with wind warnings current for today
The wind forecast provides a summary of the average wind speed and direction ranges expected within the Coastal Waters zone, covering the area out to 60 nautical miles, and indicating any changes during the day.
- Details on times of the day when winds increase above the 15 knot thresholds are given priority to assist small boat safety.
- Specific details of wind changes are provided during wind warning situations.
- Information about seabreezes is included when possible.
- Geographical information is given priority when an area is expecting lighter or stronger winds than the surrounding area.
- Details of lighter winds during the morning are provided when significant.
Seas are the waves or chop generated by the local wind conditions. The sea wave height may change significantly in conjunction with changing wind conditions.
The most dominant swell height and direction is described. Details of significant changes in swell heights during the day are provided. The swell height ranges generally cover the variation between inshore and offshore areas.
Second Swell (when applicable)
For many parts of Australia, there is generally one dominant swell. However, in some areas such as Bass Strait and East Coast Australia, two swells may be experienced by boaters within a Coastal Waters zone. A second swell is included when both swells are above 1 metre. Crossing swells may make boat handling more difficult, and pose heightened risk on ocean bars.
Find more information, view our Second Swell page.
Weather conditions that lead to reduced visibility or lightning risk are given priority. These types of conditions include heavy rain, thunderstorms, fog and smoke. The expected time periods for these weather conditions are also included when relevant.
Caution section (when applicable)
The caution section is activated whenever hazardous wave conditions pose heightened risk to boaters crossing ocean bars or for people undertaking rock fishing.
Due to the large domain of a Coastal Waters zone, it is not possible to describe all the expected conditions that may occur within the Coastal Waters zone over the course of the day or across geographical areas such as north vs south, or inshore vs offshore. Forecast maps on MetEye provide this localised detail.
Forecasts of winds
Wind direction and speed are determined by the patterns of highs, lows and fronts seen on weather maps and by local effects such as seabreezes and thunderstorm downdrafts. Closely spaced isobars (lines of equal pressure on weather maps) are indicative of strong winds. That is, the higher (or tighter) the pressure gradient, the stronger the wind speed.
Stronger wind speeds are associated with tropical cyclones, deep lows and cold fronts. Sudden squalls are associated with thunderstorms, heavy showers or the passage of a cold front or low pressure trough and can happen in clear skies (e.g. the Southerly Buster in NSW). The very strongest winds are caused by tropical cyclones, deep midlatitude low pressure systems and tornadoes/water spouts.
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
Because of the apparently chaotic situation of waves propagating in different directions and changing in character as they move, the Bureau of Meteorology uses statistical analysis when forecasting sea (wind) waves and swell wave conditions.
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. For more details, click on the Bureau's Glossary of Terms, for a description of sea and swell parameters.
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.