One of the strongest El Niño events on record is intensifying in the Pacific and is set to bring a warm, dry and unusually windy spring to much of the North Island, forecasters say.
Earth Sciences NZ's seasonal climate outlook, released on Wednesday, said El Niño had "strengthened considerably since mid-winter" and was on track to reach the very strong category early in September, with a peak most likely in late spring or early summer.
The outlook said the event was "already comparable to 1997 and has shown the strongest warming trend on record", and remained likely to verify as one of the strongest ever measured.
El Niño events are now more than 36% stronger than before the industrial age, a study in the journal Science found, with lead author Julia Cole linking the trend to human-caused warming.
1News meteorologist Dan Corbett explains what to expect as we enter spring. (Source: 1News)
It said El Niño was expected to favour "periods of active westerlies, unusually windy conditions, and greater temperature variability" over the coming months, with the effects more pronounced than in a typical spring.
Above average temperatures are most likely for the east and north of the North Island, where the outlook put the odds of a warmer-than-usual season at 50%. Rainfall is most likely to be below normal across the north and east of both islands, while the west of the South Island is very likely to be wetter than normal, at a 60% chance.
A dry North, a stormy South
The forecast points to a clear split across the country. Heavy rain systems arriving from the north are expected to become less frequent, with the greatest risk of significant weather instead coming from the Tasman Sea or Southern Ocean, and heavy rain more likely for the south and west.
The outlook warned of consequences for water users after a dry winter, saying many regions were "likely to experience reduced rainfall, more frequent dry spells, and enhanced drying of soils and vegetation, creating challenges for water-reliant sectors".
Despite the warmth, the outlook cautioned that occasional cold outbreaks were still expected through spring, and that forecasters were watching for a sudden stratospheric warming event over the pole until the risk eased in October. A similar event in 2025 had effects that lingered into December.
Out-of-season tropical cyclones in the southwest Pacific are extremely rare between July and October, the outlook said, but when they do form it is almost always under El Niño conditions. The tropical cyclone season formally begins on November 1, and forecasters said active monitoring was in place, though the risk was not currently factored into the outlook.
The ocean has flipped from La Niña to a fast-intensifying El Niño in a matter of months, with more profound impacts expected for New Zealand. (Source: Supplied)
Coastal seas remain warmer than average around much of the country, with marine heatwave conditions continuing around the South Island and Tasman Sea. Sea surface temperatures off the west of the South Island were running more than a degree above the long-term average to August 30.
Forecasters rated their confidence in the rainfall outlook as medium-high and in the temperature outlook as medium, noting the main uncertainty was whether a cooler southwesterly pattern or a milder northwesterly one would dominate.
Seasonal outlooks indicate the likelihood of conditions being above, near or below average for a three-month period and are not a substitute for day-to-day weather forecasts.
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