By Philip Duncan, WeatherWatch senior forecaster
This article first appeared in our sister publication, Dairy Farmer.
You know it’s wet underfoot when 15mm in winter is forecast and you get a rash of complaints. Despite a bit of a balancing act over recent months to dry things out, many regions are still leaning wetter than average as we hit the halfway mark of 2023.
The very wet start to the year has only partially broken, with rain frequently falling in eastern and northern parts of both main islands, similar to the first half of the year but not as intense.
Despite the El Niño building we’re still in a neutral, and therefore chaotic, set-up.
Every scientific indicator we monitor suggests El Niño is not only building, but it’s looking quite intense. The weather pattern around New Zealand and Australia is showing some signs of this developing, though for NZ in particular it’s not yet locked in.
The procession of low pressure zones from the Tasman Sea is a little unusual for this late in the year. Sure, we get lows from the Tasman all year round but normally by now we’re seeing more Southern Ocean storms too.
The shape of the high pressure zones over Australia and NZ has – for now – protected NZ from too much cold, but the downside from that is it’s giving us more northerlies (warmth) and rain. In fact the warmer set-up incredibly saw most regions either entirely frost-free in autumn or very close to it.
The many northerly, easterly and westerly quarter winds are all pushing our nationwide temperatures up, even despite a brief frosty burst of weather on the week of Fieldays (for example we had -5degC between Taupo and Rotorua, and -7degC in Central Otago).
Despite the wet and the mud, we’re also trying to cautiously warn of a sudden reversal later this year. While RuralWeather.co.nz loves to mention that “New Zealand is mostly two mountainous islands partially in the roaring forties, so anything can happen”, the global trend of both El Niño and a Positive Indian Ocean Dipole means Australia and NZ may see a drier trend emerging over spring and summer.
Our location on Earth gives us that fantastic silver lining that allows us to say we might buck the international trend and not have a super dry El Niño, but we do need to be mentally prepared for that dry – as early as now, while it’s still wet and muddy.
By the way, the Indian Ocean also has a type of “La Niña / El Niño” climate driver, called the Dipole. Like we’re seeing with El Niño emerging, we’re also seeing a Positive Dipole emerging and that encourages dry weather along the eastern side of the Indian Ocean too – a potential dry double whammy for Australia this spring and summer with drier than usual conditions expected on both the western and eastern sides of the continent.
Some Indian Ocean rainmakers do eventually make it to NZ, not a huge amount, but enough to be noticeable whenever the odd tropical depression crosses the western side of Aussie and ends up coming out near the Tasman Sea or Southern Ocean. So having a drier set-up over the eastern Indian Ocean as well as the western Pacific Ocean is possible in the months ahead.
But again, it’s all about our location, location, location. Our small size, our mountains and ranges and our isolated location out at sea mean NZ can buck some international climate trends. A good and recent example: we just had three La Niña events but only the last one brought extra rain (the previous two brought North Island droughts).
So despite the usual dry concerns over El Niño, it is good for the soul to remember that our location on our Earth means NZ can get sudden surprise rain when we should be in drought. It’s a silver lining to hold on to as we face some weather uncertainty this spring and summer.