Every experienced skipper will tell you that weather and ocean conditions can change in an instant. That’s why determining ideal boating conditions is more than just checking the three-day forecast.
Every boating trip requires careful planning, which should include a detailed analysis of the weather conditions — like you’ll find on the charts and forecasts issued by the Bureau of Meteorology (BOM). Follow these five vital weather safety checks before you head out, and you’ll be a seasoned mariner in no time!
1. Marine warnings
In terms of boating dangers, the Bureau of Meteorology (BOM) issues a range of warnings that are updated regularly to alert you if dangerous waves, winds, surf and/or abnormally high tides are expected. Their services include:
- National Warnings Summary webpage
- Marine Wind Warnings
- Severe Weather Warnings
- Hazardous Surf Warnings
- Ocean Wind Warnings for the High Seas
2. Changing weather
You should also take note of weather forecasts that can indicate reduced visibility due to rain or fog, and assess your risk to comfort and safety due to lightning, thunderstorms and squall conditions. Other forecasts include information on UV levels, so you know when to up the sun protection. All local and coastal waters forecasts can be accessed on the Marine & Ocean webpage.
Other weather hazards to be aware of in terms of boat safety include:
These pose a significant danger to mariners due to extreme winds, huge waves, thunderstorms and torrential rain that can cause poor visibility. Always check the warning services for tropical cyclones, and if you need to read up on your cyclone knowledge, there is also lots of info available online about how they develop and their impacts.
Thunderstorms are pretty common across Australia and can generate lighting, hail, waterspouts, heavy rain and strong, squally winds that can reduce visibility. They can be associated with the passage of a tropical depression or a frontal system, and sometimes they form over land and move out to sea. Mariners should refer to the Marine and Ocean web page for coastal waters forecasts, including the likelihood of thunderstorms.
It’s also important to check the Severe Thunderstorm warnings for capital city areas. These can give you more information about whether thunderstorms have been forecast for local waters areas. They are typically issued when heavy rainfall, large hail, tornadoes and wind gusts exceeding 48 knots are expected. The BOM website also provides information about how thunderstorms form – it’s fascinating reading!
East Coast lows
East Coast lows are intense low-pressure systems which occur several times each year off Australia’s eastern coast — mainly in southern Queensland, eastern Victoria and NSW. They can produce heavy rainfall, gale to storm-force winds, powerful waves and storm surges — not ideal boating conditions!
Cold fronts are boundaries between a cold and warm air mass. These can cause showers, heavy rain, thunderstorms, hail, strong to gale-force winds and gusty conditions. Winds tend to be northerly before the front approaches and then southerly or westerly behind it. Mean sea level pressure charts can help you understand more about how cold fronts work.
Sea fog is a significant hazard to mariners because it can be long-lasting and extensive. Visibility can be reduced to less than 100 metres, making navigation difficult. Fog also greatly increases your risk of a collision with other vessels or obstacles.
These are spinning columns of water and air and can be extremely dangerous — much like the tornadoes we sometimes see over land. You can read more about them (and we highly recommend you do!) in the BOM’s Storm Spotters’ Handbook.
Regular events in the Tropics during the wet season, monsoons are large-scale wind and rain events. They can persist for days on end and are associated with the inflow of moist west to north-westerly winds into the monsoon trough. They produce heavy rainfall and convective cloud formations over northern Australia.
3. Wind conditions
The wind is responsible for creating waves and swell, and the easiest indicator of sea conditions is wind speed. Wind speed is measured in knots, which are based on nautical miles. Five-knot winds or less will be barely noticeable, and you should have calm seas and ideal boating conditions. At ten knots, the surface can become choppy, which is usually OK for inshore boating. However, conditions start to get rough from fifteen knots or more, so unless you’ve got a very big boat, it’s best to avoid heading out!
Marine wind warnings are issued whenever strong winds, gales, storm force or hurricane-force winds are expected and can help you understand dangerous conditions. Local wind regimes can make conditions rough in certain areas, for example, the Southerly Buster along Australia’s east coast.
Wind gusts are typically 40 per cent stronger than the average wind speeds that are provided in marine forecasts. Squalls and thunderstorms can produce much higher gusts. A squall is a large and abrupt increase in wind speed that usually lasts for a few minutes and then diminishes suddenly. Wind gusts in a squall can exceed 40 or 50 knots, so avoid these conditions!
4. Wave conditions
As a general rule, knots don’t directly correlate into seas and swell – they are driven by tides and currents and vary almost independently. However, a five-knot day will generally accompany seas ranging from 0.4 to 1 metres.
On a day of ten to fifteen knots, you could expect seas of around 1.2 to 1.4 metres — this is quite choppy, and coupled with swell can be uncomfortable and even dangerous.
Large waves originate from intense weather systems, and they can be steeper, higher and more chaotic than usual. This can make conditions dangerous for boating, especially closer to the coast where waves enter shallow water. Wave-recording buoys provide real-time wave information in most states, and the BOM’s marine forecasts include information about the expected heights of waves.
Long period swells are typically generated by low-pressure weather systems and can travel for hundreds of kilometres from where they were formed. In deep water, these low, long swells aren’t an issue, but when they approach shallow water, they break powerfully.
BOM provides a range of services that provide wave information. You can check these by reviewing the swell and seas section of your coastal zone, or by checking out the forecast map MetEye and selecting the Waves Forecast. Warnings about larger waves are also available for Hazardous Surf conditions, which are targeted at boaters, swimmers and rock fishers.
5. Tide times
Knowing when low and high tides will occur is crucial for boats entering and exiting crossing bars and river entrances. The combination of a low tide or outgoing tidal flow can cause waves to become steeper than usual, making navigation difficult. Changing tides during the day can cover reefs or rock platforms at high tide and then expose them, which can create hazards at low tide.
You should also be aware of king tides. These are exceptionally high tides and are a natural part of the tidal cycle that vary by location and between years.
What to do if you’re caught in less-than-ideal boating conditions
Conditions vary depending on where you’re boating, and you’re unlikely to encounter dangerous conditions if you are in calm waters that are protected from the wind. Unless you’re caught in a storm of course and out at sea! If you are, make sure everyone is wearing a lifejacket (if you’re not already), and ensure all your safety gear is within easy reach.
If you can find safe anchorage in a bay or behind an island, carefully navigate your way there. If not, aim to tuck into the lee of a reef or shoal. If you’re in entirely open water, secure the deck and motor steadily into the oncoming waves. If they’re particularly large, you can tack into each wave on a slight angle. Above all, remain calm. Bad weather often passes just as quickly as it arrives. Get amongst it!
- 2020, Hazards, warnings and safety, Australian Government, Bureau of Meteorology