Marine weather forecasts

Keep an eye on the weather

Many fatal boating accidents happen in bad weather. Weather conditions can make the difference between an enjoyable day out and an uncomfortable or even tragic trip.

If in doubt, don't go out!

A large proportion of accidents involving small vessels are weather related. Bad weather makes the environment onboard a vessel extremely hazardous. It also places a lot of strain on the vessel’s structure and equipment and the people on board.

It is important to respect the weather at sea. Skippers should make sure they understand the different parts of a weather forecast and the best way to find up-to-date local information.

Your guide to the weather

Your guide to local and coastal marine weather forecasts

Sources of marine forecast

MetPhone Coastal

Navigation and weather warnings

Your guide to the weather

Check the marine forecast

Marine weather forecasts state what the weather is expected to do. Always check the weather before you go out boating using a marine weather forecast. Land and general forecasts do not take into account wind speed over water (which is double that over land) or the waves or swell. If a land forecast does give wind speed, it is in km/hr and that is an indicator that you are listening to the wrong forecast.

Check the weather [MNZ's Boatsafetyinnz YouTube channel]

Go local

While marine forecasts are almost always accurate when predicting major weather events, such as gales, they can be less accurate when predicting local changes of conditions, so you should always be prepared for the unexpected. Seek local knowledge from those who live in the area – harbourmasters are an excellent source of local information.

Coastguard NowCasting

Wind data is captured at selected sites around New Zealand and then broadcast continuously over dedicated marine VHF channels. This information is updated every minute and broadcast continuously, along with the latest weather forecast and tides. Text message updates are available for some areas. NowCasting reports the actual conditions in each place rather than the predicted conditions in the forecast. Coastguard NowCasting is a service provided free of charge to boaties.

Coastguard NowCasting location map

Take a long view

If you are planning ahead or intend to be away for a day or two, get a long-range weather forecast. The outlook will tell you what weather is predicted up to 5 days ahead. Having information in advance leaves plenty of time to alter plans or decide to wait for better boating conditions. The 7-day isobar/rain maps are good for planning and are available on www.metservice.com.

Prepare for the unexpected

Remember that the weather can change suddenly and without warning. Keep an eye on the weather while you’re out, listen to the NowCasts in your area so you get a warning of increasing winds before they arrive, and head for shelter at the first sight of worsening weather. When the wind starts to blow, the water becomes very rough, very quickly, especially on lakes and rivers.

Remember that forecasts are only the best prediction available at any given time.

Your guide to coastal and local marine weather forecasts

  • Areas – Most boating areas are covered by the recreational marine forecast, and coastal forecasts cover the area out to 55 miles (100km) offshore. Details of the current wind strength can be heard on VHF radio.
  • Situation – A description of position and movements of highs, lows and frontal systems expected to affect the New Zealand coast within the next 36 hours. It also names areas affected by warnings.
  • Outlook – All marine forecasts are for up to 48 hours, with the outlook for a further 3 days.
  • Outlook – All marine forecasts are for up to 48 hours, with the outlook for a further 3 days.
  • Forecast details – A description of the expected average conditions over open water for the next 24 hours.
  • Wind – Direction, such as north-west, is the direction the wind is expected to come from. Direction is given in knots. This is an average speed so you can expect that gusts may be 50 percent higher. Funnelling between headlands can cause the wind speed to double.
  • Sea – A description of the waves formed by the local wind.
  • Wave height – Used in forecasts and refers to the size of the significant waves (average, from trough to crest, of the top third, or highest in each average set of 7 waves) that are generated by the wind in the area.

The approximate wind wave height measures used are:

  • calm – up to 0.1 metre
  • smooth – up to 0.5 metre
  • slight – up to 1.0 metre
  • moderate – up to 2.0 metres
  • rough – up to 3.0 metres
  • very rough – up to 4.5 metres
  • high – up to 6.5 metres
  • very high – up to 8.5 metres
  • phenomenal – up to 11.0 metres (or more)

Note: the occasional wave (1 in 100) is 50 percent higher, and the maximum wave (on average once a day) is twice the size of the significant wave.

  • Swell – Comes from either a distant disturbance, such as a cyclone or depression, or develops from wind waves that have been blowing from the same direction for a length of time. Swells increase in height and get steeper when they reach shallow water.

The measures used for swells are:

  • low – under 2.0 metres
  • moderate – 2 –4 metres
  • heavy – over 4 metres
  • Visibility – Given when visibility is expected to be less than 10 kilometres. The average visibility in New Zealand is about 15 nautical miles.

The visibility distance are:

  • fog – less than 1.0 nautical mile
  • poor – 1–3 nautical miles
  • fair – 3–6 nautical miles
  • good – over 6 nautical miles
  • Warnings – These are issued for gales or storms anywhere on the New Zealand coast. A strong wind warning may be included in local area forecasts if wind gusts are expected to reach 33 knots (about 60 kilometres per hour).
  • Wind speed – Wind speed is given in knots and the direction given is where the wind comes from.

Wind warnings are issued as follows:

  • strong – the wind is expected to exceed 25 knots as a steady wind or 33 knots in gusts
  • gale – expect 33 to 46 knots as a steady wind – gusts can be 50 percent higher
  • storm – 47 knots or more as a steady wind – gusts can be 50 percent higher

Note: if the winds are associated with a cyclone from the tropics this will be mentioned in the warning, but tropical cyclone warnings are not issued in New Zealand.

Sources of marine forecast

The most convenient sources of marine forecasts, including the 5-day outlook are:

  • VHF radio – the MNZ maritime radio service provides forecasts announced on channel 16 – call at 0533, 0733, 1333, 1733 and 2133 hours
  • Coastguard on VHF radio channels 20, 21, 22 and 23, including the “NowCast” continuous broadcasts in many recreational boating areas
  • MetPhone – dial 0900 999 + map area number (see map below).

Other sources of marine forecasts include:

  • The MetService Marine smartphone app
  • local Coastguard stations on VHF radio
  • www.metservice.co.nz [New Zealand’s national meteorological service]
  • private coastal radio stations and radio stations for fishermen
  • local newspapers – but remember they can be published many hours earlier and are often out of date
  • local radio stations, especially in summer
  • on National Radio at 0400 hours.

MetPhone coastal


Navigation and weather warnings

Navigation and weather warnings alert mariners to potential dangers and risks. Coastal navigational warnings, radio navigational warnings, NAVAREA XIV warnings and meteorological warnings. Read more