Weather

Find out about current forecasts, sources of weather information, synoptic charts, wave and sea breeze information.

  Check the weather before you go out on the water

Before actually starting your trip, get the most up to date forecast available.

We recommend that you read the forecast and warning information on the Marine Weather Services page of the Bureau of Meteorology (BOM) website. You should also read the Marine Weather Services pamphlet available on their website.

Other sources of weather information are detailed in the next section.

External Link Bureau of Meteorology (BOM): Check the weather before you go out on the water
External Link Bureau of Meteorology (BOM): Terminology
External Link Marine Safety Tasmania: MetEye - Weather forecasting tool from the BOM (video)

  Sources of weather information

Internet

A full range of weather information is available on the Bureau of Meteorology website.

Public broadcast radio/television

The Bureau of Meteorology sends coastal waters forecasts and warnings to most radio and television networks in the city and country. The stations usually announce the time the Bureau issued the forecast, this is important, as older forecasts are less valuable.

Marine radio

External Link Australian Communications and Media Authority (ACMA): Using VHF Marine Radio for weather information
External Link Bureau of Meteorology (BOM)

Marine radio weather service

Broadcaster VHF Channels Broadcast times
WA Water Police weather and navigation warnings (within 20 nautical miles of Perth metro area) 16 and 67 0718 and 1918 hours WST
Volunteer sea search and rescue groups 16 and 67 and/or 27.88 MHz Within normal recreational boating hours
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The Bureau of Meteorology also provides a limited VHF weather service for some parts of regional WA. For VHF frequencies and broadcast times for Carnarvon, Esperance, Geraldton and Broome, visit the Bureau of Meteorology VHF Marine Weather Services page.

Recorded telephone services

The Bureau of Meteorology has recorded services via Weathercall for coastal waters forecasts and warnings.

Services include:

External Link Bureau of Meteorology (BOM): Communication services

Weathercall services

Service Telephone No.
Full State Service 1900 955 366
Perth Metropolitan Service 1900 926 149
Perth Local Waters Service 1900 955 350
WA Marine Service 1900 926 150
Northern WA Coastal Waters Service 1900 969 901
Western WA Coastal Waters Service 1900 969 902
Southern WA Coastal Waters Service 1900 969 903
WA General Warnings Service 1900 955 371
WA Tropical Cyclone Information 1300 659 210
WA Coastal Marine Warnings 1300 659 223
View full screen table

Note: Standard call rates apply for 1300 numbers. Calls to 1900 numbers cost 77c/minute including GST. Higher rates may apply when using mobile or payphones.

Weather by fax

The Bureau of Meteorology's Weather by Fax service provides forecasts, observations and warnings including weather charts (updated three hourly), satellite photos (updated hourly), weather radar reports, the latest warnings, routine coastal waters forecasts and the latest actual reports.

Set your fax machine in poll receive mode and dial 1902 935 200 for the main directory.

Publications

The Bureau of Meteorology also produces useful pamphlets and booklets including:

  • Marine Weather Services.
  • Tropical Cyclones.
  • Wind, Waves and Weather for Perth Waters.

These are available on the Bureau of Meteorology website.

  Understanding forecasts

A forecast gives a general description of the expected weather in the forecast period plus outlook including warnings and other specific information.

Strong wind warnings

Small craft warnings of strong winds are issued whenever mean wind speeds exceeding 25 knots are expected. For any mean wind speed forecast, gusts can be 40 per cent higher, so the very smallest of strong winds will produce gusts of 35 knots.

Severe weather

The northwest of Western Australia is one of the most cyclone prone coasts anywhere in the world. The cyclone season extends from the months of November through to April, but most of the coastal impacts occur between January and March.

No vessel should be at sea within several hundred miles of a cyclone.

Wind strength and direction

You are interested in wind speed and direction mainly because of the waves the wind will build. Wave height depends on:

  • Wind speed.
  • Length of time the wind blows (duration).
  • How far over the water it blows (fetch).

Wind off the land will produce smaller waves inshore because of the limited fetch; they will also be steep and close together, a feature of short fetch. If you operate in the shelter of islands you will also get smaller waves than the forecast, which assumes no shelter.

  The weather map, synoptic charts

You normally see the weather map (also called a synoptic chart) on television or in the newspaper. It will usually be older information than you can get from other forecast sources, but it gives a good picture of what is happening and is likely to happen.

Winds

Wind is caused by the movement of air from high pressure to low pressure systems, but it does not flow directly from one to the other. It blows more nearly along the pressure contour lines (called isobars) you find on weather maps.

In the southern hemisphere this is in a clockwise direction around low pressure systems and anti clockwise around highs.

The bigger the difference in pressure of the systems, the stronger the wind. The number of isobars, and their closeness to each other, indicate the pressure differences.

When estimating the progress of the pressure systems, you can reasonably assume that a low will move the width of Australia in two or three days.

Cold fronts

The line with spikes on it is a cold front, commonly associated with winter lows. Ahead of the front you can expect squalls followed by rain. The wind typically changes direction at the front (shown by the bend in the isobars) and strengthens.

Wave information

Wave height depends on:

  • The length of time a wind blows.
  • How far over the water it travels, so easterlies and local sea breezes make smaller waves than steady winds off the ocean.

Above 15 knots there will be many whitecaps and some spray. Swell waves are independent of existing wind. They are decaying waves usually produced by strong winds in distant blows.

Though smooth and harmless looking, they travel very quickly and can create big breakers in shallowing water.

Sea breezes

Local winds such as sea breezes blow for only a few hours over waters close to shore, so the waves they cause are lower than the large scale winds. However, if the sea breeze blows from a similar direction to the existing wind, it will join forces and build bigger waves.

Sea breezes are a near shore event caused by the heating of land during the day. Their strength will be partly dependent on the existing (synoptic) wind. On the west coast sea breezes come from the south west, so they will be opposed and weakened by a synoptic north easterly. The further towards south the synoptic wind, the more it will assist and strengthen the sea breeze.

 

Page last updated: Tue Dec 2 2014 9:02:41 AM