Sunshine Coast boating weather: how to read the marine forecast

The forecast to read: BoM's Sunshine Coast Waters Forecast

The Bureau of Meteorology (BoM) covers this stretch of coast in its Sunshine Coast Waters Forecast: Double Island Point to Cape Moreton. It's one of Queensland's coastal waters forecasts. Moreton Bay, to the south, has a forecast of its own, so check that one if your trip heads that way.

Coastal waters means within 60 nautical miles of the coast. Inside that, BoM splits the water in two. "Inshore" is from the coast out to 12 nautical miles. "Offshore" is 12 to 60 nautical miles. A line like "1 metre inshore, increasing to 1 to 1.5 metres offshore" tells you the water gets bigger the further out you go.

In Queensland, local and coastal waters forecasts come out at about 3 am, 9 am, 3 pm and 9 pm. Each covers 3 to 4 days and gets updated again if conditions change a lot. The page also says when the next forecast is due, links tide predictions, and links to current Queensland warnings at the top.

Wind is in knots, named for where it comes from, and gusts run 40% higher

Every wind line gives a direction and a speed in knots, such as "East to southeasterly 10 to 15 knots". The direction is where the wind is coming from. A northerly blows from the north towards the south. BoM uses the same rule for swell.

The speed is an average. BoM measures it over 10 minutes at 10 metres above sea level. Real wind comes in gusts and lulls around that number, and gusts in any 10 minutes can be 40% higher. BoM's own example: a 25 knot average can bring 35 knot gusts.

Squalls are worse. A squall is a sudden jump in wind that lasts a few minutes, often with a cold front or thunderstorm, and its gusts can top 40 or 50 knots. Watch the time words too. "In the morning" means 1 am to 11 am, and "during the afternoon" means 1 pm to 9 pm. So a forecast of wind "turning northerly in the evening" means after 6 pm.

Seas are local chop, swell comes from far away, and some waves hit twice the forecast

The forecast lists seas and swell separately because they're different waves. Seas, or chop, are made by the local wind right now, with short gaps between crests. Swell was made by wind in a distant system. It can travel thousands of kilometres, and you can get swell even when the local wind is light.

BoM's heights are significant wave heights: the average of the highest third of the waves. Seas and swell don't simply add up. A 1.5 metre sea and a 1.5 metre swell make a total wave height of 2.1 metres, not 3.

Then plan for the odd big one. BoM says about one wave in every 2000 to 3000, or 3 to 4 times a day, will be about twice the total wave height. Long period swell usually isn't a problem in deep water, but it slows down and gets steeper and higher as it reaches shallow water. In shallow bays, chop crests sit closer together, which BoM flags as a hazard for smaller boats.

Marine wind warnings start at 26 knots: strong wind, gale and above

BoM issues a marine wind warning for local and coastal waters whenever average winds of 26 knots or more are forecast. There are four levels:

- Strong Wind Warning: averaging 26 to 33 knots - Gale Warning: averaging 34 to 47 knots - Storm Force Wind Warning: averaging 48 to 63 knots - Hurricane Force Wind Warning: averaging 64 knots or more

Warnings come out up to 42 hours ahead, or any time conditions build fast. They're updated every 6 hours and cancelled once things ease. Remember these are averages too, so a strong wind warning at 30 knots can mean gusts above 40.

Two other warnings matter on the water. A Severe Thunderstorm Warning covers large hail, heavy rain, tornadoes or damaging gusts, generally over 48 knots (90 km/h). A Hazardous Surf Warning is for boaters, rock fishers and swimmers at risk from large swells and waves. BoM says to use a warning to decide whether it's safe to go out, whether to change plans, or whether to head back and find shelter.

Tides change the water: check the times and watch for wind against tide

Tides change depth, currents and how the waves behave, so check them with the forecast. BoM publishes tide predictions for Mooloolaba, Noosa Head, Caloundra Head and Bribie Island (Bongaree), among other Queensland places.

A few points from BoM help. Water levels rise quickest around mid-tide, and the strongest currents come at mid-tide too. Tide times change every day. The weather can push the actual water level above or below the prediction. When the tidal current runs one way and the wind blows the other, waves get steeper and closer together, which can turn a fair day choppy at the wrong time.

The BoatSafe Workbook adds that tide times run almost an hour later each day. Spring tides, around the full and new moon, bring very high highs and very low lows. Depth at any spot is the chart depth plus the tide, so a channel you used at high water may be shallow at low water. Plan your return before the tide leaves you short of water.

When to stay in sheltered water: whitecaps offshore mean stay inside

The BoatSafe Workbook gives a plain rule: if you can see whitecaps offshore, stay in sheltered waters. It also says that if it looks dicey, don't go out, and if it starts to turn, head straight for shelter.

The Workbook explains why the afternoon often gets worse. As the land heats up, winds tend to blow onshore in the afternoon and, particularly in summer, can become quite strong. In summer, that can also help build thunderstorms along the coast in the late afternoon. Morning winds tend to be offshore and tend to bring better sea conditions.

Wind keeps working on the water, too. Under a steady wind, the Workbook says seas can roughly double in size over 12 hours. The further wind travels across water, the bigger the waves, so the lee side of a large bay stays smaller. If the wind is due to rise, plan to finish upwind of your home shelter, so the run back is downwind and easier.

Go or no-go: run BoM's five checks before you leave

BoM sums up marine weather safety in five vital checks. Run through them before every trip, then keep watching once you're out.

1. Marine warnings. Is there a strong wind, gale or thunderstorm warning for your area or time on the water? 2. Changing weather. Does the forecast show a wind change, a front or a chance of thunderstorms during your trip? 3. Wind conditions. What's the average, and what will 40 percent gusts feel like in your boat? 4. Wave conditions. What are the seas and swell, and could a wave twice that height catch you out? 5. Tide times. When are high and low water, and will the wind be against the tide when you come home?

BoM is clear that safe conditions depend on your activity and your boat, so there's no single number that suits everyone. The BoatSafe Workbook adds: on the water, watch for darkening and lowering cloud, whitecaps, a changing sea and a falling barometer, and if conditions get worse, put lifejackets on. Our life jacket rules guide covers who must wear one. And if in doubt, BoM says, return home.

Getting the forecast on the water: phone, VHF Channel 67 and MarineLite

Queensland's weather is changeable and unpredictable, the Queensland Government says, so keep checking once you've left. The BoatSafe Workbook notes that marine radio, broadcast radio and a mobile phone can all work afloat.

Maritime Safety Queensland's weather service provides Bureau of Meteorology weather information for the cost of a local phone call:

- All of Queensland: 13 00 36 04 26 - Marine warnings: 13 00 36 04 27 - South-east Queensland: 13 00 36 04 28

Local volunteer marine groups also broadcast the weather on VHF Channel 67. BoM's MarineLite gives text-only marine forecasts and warnings, and MetEye shows wind and waves on a map. One catch: most coastal weather stations sit on land, so their wind readings may not match what you're getting out on the water.

If someone's life is at risk, call Triple Zero (000), Australia's number for life threatening or time critical emergencies. For the wider set of rules every skipper follows, see our Queensland boating rules guide.

Learning to read the weather on the BoatSafe course

Weather and tides are part of BoatSafe training. The BoatSafe Workbook, the Department of Transport and Main Roads' official guide to the licences, has a section on each. Our Boat Licence course is priced from $329: a one-day course with online theory included and all equipment provided, run by experienced local instructors on sheltered Sunshine Coast water.

You'll train at one of three venues: Golden Beach in Caloundra on the Pumicestone Passage, Maroochydore on the Maroochy River, or Noosaville on the Noosa River. Pick a day that suits you on the course dates page, and read how to get a QLD boat licence for the steps from course to licence.

Training is delivered by Australian Boating College.