New Zealand meteorologist explains the incoming El Niñoño shift and what it means for winter weather
A daily news podcast from the New Zealand Herald interviews a meteorologist about the transition from La Niñaña to El Niñoño and its implications for New Zealand.
Summary
Chelsea Daniels of the New Zealand Herald's The Front Page podcast speaks with John Tunster, a meteorologist from Earth Sciences New Zealand and MetService, about the rapid shift from La Niñaña to El Niñoño conditions expected to affect New Zealand this winter. Tunster explains that climate models show a greater than 60% probability of a strong El Niñoño event by spring, with the potential to intensify further. He notes that the speed of this particular La Niñaña-to-El Niñoño transition is historically unusual, with very few comparable events on record, making forecasting more difficult. For New Zealand, the primary expected impact is enhanced westerly and southwesterly winds, producing drier conditions in eastern and northern areas — a marked contrast to the wet, northerly-driven winter of the previous year.
Key Takeaways
FULL TRANSCRIPT
Introduction and the difference between La Niñaña and El Niñoño
Chelsea Daniels: El Niñoño is set to hit New Zealand this winter. Global climate models show there's a greater than 60% probability that this event will be strong by spring, with the potential to intensify later this year. But what does that actually mean? What happens when the ocean surface warms? And what does it mean for our weather? Today on The Front Page, Earth Sciences New Zealand and MetService meteorologist John Tunster is with us to make sense of it all. First off, John — and just to preface this by saying I ask this every single time we do something on this subject — what is the difference between La Niñaña and El Niñoño?
John Tunster: It's a totally fair question. They sound pretty similar to us. They're Spanish words, but they are completely different phenomena. Effectively, we are talking about a global phenomenon here. We're looking at the tropical Pacific Ocean. El Niñoño is warmer than normal waters in a certain part of the tropical Pacific Ocean, whereas La Niñaña is colder than normal waters in that same region. It seems like a pretty small thing, but it initially has local impacts in that area — around South America and the tropics — and those impacts just cascade around the world very often.
The unusual speed of this La Niñaña-to-El Niñoño transition
Chelsea Daniels: How unusual is the speed of this shift from La Niñaña to El Niñoño? Does that tell us anything about what's coming up?
John Tunster: That's a great question, because we've been monitoring this potential for quite a while — actually since even the end of last year. When you go back and look around, there aren't a huge number of what we would call historical analogues for a switch that occurs from La Niñaña to El Niñoño in the same year, and certainly not for one that occurs as quickly as this. So we're really running quite light on analogues, to be honest. When we searched through the record, we were able to find 1976 possibly as one, and 2023 to 2024 was another. But the trouble is, when you look at these historical analogues, there's a whole bunch of other variables that change within them. So it can't necessarily be the case that we just follow history and know what's coming in the future.
What a "strong" El Niñoño means in practical terms
Chelsea Daniels: When we're talking about a potentially strong El Niñoño, what separates a strong event from a moderate event in practical terms?
John Tunster: We use a cutoff, which is effectively the anomaly of the sea surface temperature in a particular box in the Pacific. When it hits a certain threshold, that gets counted as moderate or counted as strong. It's quite a binary sort of cutoff, and that's just how it's done. It doesn't necessarily mean that the impacts around the world from all strong El Niñoños are the same, or all moderate El Niñoños are the same. Sometimes we can have just a moderate El Niñoño that has quite a decent effect on New Zealand.
What the modelling is showing and expected global impacts
Chelsea Daniels: What is the modelling telling us at the moment? What should we expect from this change?
John Tunster: We should probably start by looking in the tropics itself, because that's the thing that's really catching our attention. As it stands, this El Niñoño has not started yet — it's something in the future. What's interesting is that all of the models we look at are forecasting a very dramatic increase in sea surface temperatures in that region. This consensus is growing and we think it's a believable consensus. We double-check these model forecasts up against what's happening in reality and we can link up known precursors with what the models are saying. We just want to make sure that we're not looking at something that's purely a modelling artefact and that it is actually related to reality. Effectively, all our simulations looking forward are showing a dramatic increase in sea surface temperatures in that part of the Pacific.
Running on from that, there will be global impacts. The question is where and when those global impacts occur. New Zealand — we do like to say we are a small corner of the world. We're expecting this El Niñoño to have global impacts, and it would be surprising if we didn't see impacts on New Zealand from this. But there will certainly be places that see impacts before us. A great example is that El Niñoño tends to map quite strongly onto the Indian monsoon, which is a really important global weather phenomenon for producing food in India, for example. The Indian Meteorological Department does a monsoon forecast every year and they're forecasting a deficient monsoon this year. So that's one of the global impacts we are expecting from this.
The impacts on New Zealand will probably be somewhere down the line. We're actually having our seasonal climate outlook meeting this afternoon, looking out to July, and we'll start trying to decide when we think those impacts might affect us. It could be during that outlook period, or it could be pushed a little bit beyond it. That's what we're trying to figure out.
What El Niñoño typically means for New Zealand's weather
Chelsea Daniels: Generally, what does El Niñoño mean for New Zealand?
John Tunster: For us, it effectively gives us an increase in westerlies. Sometimes it's more like southwesterlies, sometimes more like westerlies or northwesterlies, but it's that kind of flavour. We're very accustomed to westerlies already, of course, but El Niñoño tends to enhance them, push them out for longer, and can potentially make them more intense. What that tends to do is create a very particular rainfall pattern in general — it focuses rainfall into western areas and possibly sometimes parts of Southland, depending. Conversely, we tend to see less rainfall making it through to eastern and northern areas. That's the general pattern we would see from an El Niñoño.
It is important to note that El Niñoño — or more precisely the El Niñoño-Southern Oscillation, which encompasses both the El Niñoño and La Niñaña fluctuations — accounts for roughly around 25% of our variability. Now, 25% is not nothing, but it's certainly not everything. So we have this strong driver mapping on to what you could normally say is 25% up for grabs, whereas this time around, as this El Niñoño develops, that 25% is more like a baseline being covered by the El Niñoño. But there's a whole lot of variability that can take place on top of that.
Chelsea Daniels: So the headline here, I suppose, with those southwesterlies is that we should be expecting a drier winter — which someone living in Auckland like myself gets quite excited about, because I hate nothing more than an awful, wet, muggy winter. Five seasons in a day. I said five because Auckland just creates its own season most of the time. But a dry winter for different parts of the country looks quite different. How does that look on the ground across New Zealand?
John Tunster: It does get a little bit concerning in some areas, especially where primary industries are a very big deal. What we'll be keeping an eye out for is if things start to already dry out. The weather situation right now is looking reasonably dry for the near future, as an example. What we'd be concerned about is dryness compounding on top of pre-existing dryness — that's where you start to run into concerns.
It's tricky for places like Auckland because, as I'm sure you're aware as an Aucklander, there are lots of different types of southwesterlies. You can get pretty blustery, squally, unpleasant southwesterlies, but you can also get southwesterlies that have a drying trend — they come through and they're not really giving you any showers, they're just drying things out. So within a southwesterly flavour, there are all sorts of little variabilities that occur.
Cutting through the hype — "Godzilla El Niñoño" and similar terms
Chelsea Daniels: You may have seen those scary stories online — "Blowtorch El Niñoño," "Godzilla El Niñoño," "Ultra Mega El Niñoño," or the even more tame "Super El Niñoño." It's time to cut through the hype. The truth is there is no such thing as a super El Niñoño or any of those others, but it sounds really cool and gets lots of clicks on social media.
How quickly can this dryness — you mentioned dry upon dry — how quickly can that escalate into drought conditions?
John Tunster: That's a pretty tricky question because it comes into things like the baseline of hydrology. From a meteorological point of view, we'd be looking at things like — at this time of year, we can get dryness occurring just from a lack of rainfall. But as we've probably all noticed, the sun is getting weaker and it's also not a particularly windy time of year. Things can get more concerning if we don't get our winter rainfall, or we end up slightly deficient on our winter rainfall, and then we come into spring when we have stronger drying winds potentially and stronger sunshine. That's when we could start to see concerns. But I think that's somewhere down the line — it's something we just need to keep in the back of our minds and keep up to date with all the latest information.
Whether the rapid swing could become more common
Chelsea Daniels: In terms of the speedy swing from La Niñaña to El Niñoño — has this happened more abruptly than in the past? And will we continue to see that swing?
John Tunster: I was discussing this with a colleague earlier. It doesn't appear that we've seen this happen more frequently so far, but there is some quite recent research that suggests that what you're describing — as we push towards later in the century — could become more of a feature of our climate. The magnitude of each El Niñoño event could increase, and then the swing is sharper correspondingly.
Chelsea Daniels: New Zealand — we are kind of in the corner of the world, and we do tend to get news and current events about three to five years later than everywhere else. But does that put us in a good position, because we can see how El Niñoño affects other nations — like India, as you mentioned — before it hits us?
John Tunster: That is a good question. I think what it allows us to do is monitor what's happening with the actual event in the Pacific Ocean. We'll have a direct comparison for how well the forecasts of the actual event have been going against reality. But how things impact on us — we're so subject to the Southern Ocean and all its vagaries that I would say explicitly what happens in India doesn't really have much of a direct impact on us. But certainly we can track the development of the El Niñoño ahead of many of the impacts expected on us, and that's pretty typical for us. We're an area that sees a lot of lagged impacts from El Niñoño. Our impacts can be several months down the line sometimes from an event.
It's actually happened recently with the La Niñaña — La Niñaña has actually gone, but we've still seen some La Niñaña-type weather patterns. It can be quite tricky for us to kick off these patterns.
What New Zealanders will actually notice this winter
Chelsea Daniels: We all know the words — El Niñoño, La Niñaña. We always hear about a dry winter coming because of El Niñoño and the oceans. But what should New Zealanders really look out for? What will they notice?
John Tunster: I think you touched on it quite nicely earlier. You mentioned the type of Auckland weather you don't like — those muggy, wet situations. I think that might be a good measure of it. We've talked about this rapid switch around, so perhaps one easy comparison is that probably this winter will be different to last winter. Last winter was quite wet for a lot of places. There were a decent number of northerly-sourced, northeasterly rain events. One good example was the Nelson-Tasman flooding that happened late in June or early in July last year — that was characteristic of that type of winter. What people might start seeing on the ground is that if you've become accustomed to seeing a lot of these humid, rain-bearing events coming down from the north, maybe we just start to see far fewer of those than what we've become accustomed to over the last year.
Chelsea Daniels: So I can hold off another year from buying a rain jacket?
John Tunster: In Auckland, I have to say that would be, dare I say, slightly foolish.
Chelsea Daniels: Thanks for joining us, John.
John Tunster: No worries. Thanks very much for having me.