Boaties and seafarers will from today be offered free warnings of storm clouds brewing up to five days away.
New Zealand will become the first country to broadcast such long-range predictions on marine radio channels - a move the Maritime Safety Authority expects will reduce boating accidents and costly search-and-rescuemissions.
Although it has been possible to obtain detailed long-range forecasts on request to the MetService, these have cost money.
Free weather outlooks were for just 36 hours ahead, often making it difficult to plan the return leg of a weekend boating excursion, for example, from Auckland to Great Barrier Island.
The Ministry of Transport will pay MetService for the new forecasts, which the safety authority and regional coastguards will broadcast on marine radio channels and over the internet.
They will provide "a slightly more broad-brush approach that won't include wind speeds", said Jim Lott, the authority's manager of recreational boating. But they would give mariners a general picture of the weather, and plenty of time to change plans.
"A lot of people plan to go boating three to four days before the weekend, and until now they've known very little about what the weather is going to do," Mr Lott said.
"Anticipation of a trip can be huge - sometimes it's really hard to change your mind at the last moment if the weather's dodgy on the day. And poor weather is one of the three key factors of maritime accidents."
More than half of fatal boating accidents - which claimed 18 lives in the past 12 months - occurred in bad weather.
Although extended land-based forecasts have been available, marine outlooks are more challenging to provide as they require weather services to plot more variations, such as wind, swell and storm systems.
MetService staff derive the marine forecasts from computer modelling services in the United States, Britain, and on the Continent.
Staff take the models and compare them, then make adjustments for the unique geological features of New Zealand.
Said MetService spokesman Bob McDavitt: "It may be just an idea [of the weather], but it's the best idea going."
