Not every app uses the same data, and the best one for you might not even be produced in New Zealand. Photo: pixel-shot.com (Leonid Yastremskiy)
At last, it is spring - so what sort of weather will the change in seasons bring? To find out, most of us these days will be turning to an app.
Weather apps are big business, making money from advertising, paid upgrades and data monetisation. Global revenue by 2022 had reached $1.5 billion, and was expected to more than double by the end of the decade.
But not every app uses the same data, and the best one for you might not even be produced in New Zealand.
Dr Jim Salinger, whose work on climate science saw him named New Zealand of the Year for 2024 and part of the Intergovernmental Panel on Climate Change, which earned a Nobel Prize in 2007, recommends a couple produced in Europe - Norway's yr.no and the Czech windy.com.
The location of the apps' creators is less important than the weather models they pull information on, he told RNZ's Sunday Morning.
"The Norwegian one, they use output from the European Centre for Medium-Range [Weather] Forecasts (ECMWF) model, and that's updated every six hours and it has a grid spacing of nine kilometres - so that's the densest one that is used on these weather apps for this, and you can get hourly forecasts for the next three days, then three-hourly forecasts to 10 days out.
"That's for our part of the world… probably one of the most powerful numerical weather prediction models that we have on the planet."
"Windy is the other one, and this is a Czech company, and they have the ability if you want to compare output, you can use the American model, which is the [Global Forecast System] which [the US-based National Oceanic and Atmospheric Administration] produce; you can use ECMWF; you can use Icon, which seems to be a German one; and you can use Access… the Australian model, so it gives you a rectangular area which goes from Western Australia out to the Chatham Islands.
"And of course, Access is more tuned for us to the Southern Hemisphere conditions, so you might want to use that one if you're looking more local."
Your guide to the best weather apps
Our locally produced MetService app, Salinger said, was "quite limited in the number of places that you can get forecasts for", without the granularity offered by yr.no.
"[With] yr.no, you can be anywhere and there'll be a point near you which it's giving you output for."
But they were not without glitches which only local knowledge could fix.
"I know that there is a fault in the Norwegian one that likes to - quite often on cold mornings when there's been a clear night - put fog into Queenstown. Now, it probably isn't attuned to the quirks of central Otago. You'll certainly get fog in Clyde, Alexandra, Cromwell and Wanaka, but you don't get fog in Queenstown… What you need to do is check out the actual app with where you're living and seeing how it performs."
Here comes the rain again
August's unsettled weather saw New Zealand deluged in rain. Salinger said that was likely to keep happening in the early weeks of spring, with a La Niña event looking increasingly likely.
Jim Salinger. Photo: Supplied
"We're certainly heading the La Niña way," Salinger said. "There's no doubt about that. Northeasterlies over New Zealand and you name it, it gets rather wet in the north and east of New Zealand.
"But in Otago, Southland, Fiordland, sheltered from the northeasterlies and you've got a lot more anticyclones, those high-pressure areas tracking across the South Island to the Chatham Islands area, and it gets pretty dry there, and of course, the southern lakes go down. That's the general pattern, though La Niña may well have a surprise for us.
"In early spring the La Niña expresses itself as more northwesterlies over New Zealand - and you probably know what that means, a lot of rain in the west of the South Island and west of the North Island initially. And of course, northwesterlies will be warm, so this could well produce quite a bit of rainfall in early spring in western areas, which hopefully some of it will get into the southern lakes and it'll be mild.
"But then in November you get the switch to northeasterlies - so that's when the La Niña switch comes in. It'll be interesting to watch. Certainly in the next week, the roaring forties and furious fifties are going to keep roaring, and they're mainly westerlies and northwesterlies.
"The other effect is with the La Niña going on, it brings in warmer air flow from the northeast."
And an increasingly warmer climate meant rainfall events were only going to get worse.
"You just need to think of 2023, the Auckland anniversary floods and Cyclone Gabrielle. I think the difference is every degree the air warms - and we've warmed almost one degree since 1900 - it holds 7 percent more moisture in it. So, when it does rain, you get more flooding."
Wind of change
New Zealand was strange in that we had two government-funded forecasters - MetService and the National Institute of Water and Atmospheric Research (NIWA) - which sometimes offered slightly conflicting advice.
"NIWA has its own numerical weather prediction model and MetService would be using their model, and that could be the difference," Salinger explained.
They used to be part of the same government department, but in the early 1990s MetService was split off as a separate state-owned enterprise, while NIWA was established as a Crown research institute.
"I predicted that when it happened in 1992 we'd end up with two government-funded weather forecasting agencies - and that's what we have. Unfortunately there's been up to now, the present time, there's been three reviews because people haven't liked this arrangement - it causes all sorts of problems.
"And finally, consultants have been brought in recently and I just hope that sanity prevails because Sir Peter Gluckman has a science panel looking at how science in New Zealand should be arranged, and this would be an ideal time to put it all together rather than having duplication, which is also a hell of a waste of money."
In 2006 an independent panel recommended a merger, but ministers rejected the advice.
Salinger said a merger would improve the quality of local forecasting.
"It's just an absolute shame and missed opportunities when we were together as one in the old organisation…. we would be much better off with one. And I believe the current CEO of MetService is in favour of the recombination… This is where we're losing out big time."