Two of the world's foremost climate authorities are warning that an El Niño event is now developing, driven by unusually warm sea surface temperatures across the tropical Pacific. Earth Sciences New Zealand (ESNZ) and the World Meteorological Organisation (WMO) have both sounded the alarm, and the probabilities attached to their assessments are difficult to ignore.
In its latest overnight update, the WMO put the chance of an official El Niño emerging this winter at 80 percent, with an even greater likelihood of those conditions persisting through to at least November. ESNZ goes further still, placing the probability of El Niño conditions forming over winter at 95 percent. The agency's most recent seasonal climate outlook identifies the austral summer of 2026-27 as the anticipated peak. "Peak El Niño conditions are expected to occur during the austral summer of 2026-27, with the potential for this event to have significant impacts," the outlook summary said.
El Niño takes hold when sea surface temperatures in the eastern Pacific rise above normal, causing trade winds to lose strength and pushing rainfall toward that side of the ocean, away from both Australia and New Zealand. For this country, the typical signature of such an event is wetter than average conditions in the south-west of the South Island, while much of the rest of the country, particularly eastern and north-eastern areas, grows drier and windier.
For large parts of the North Island, this marks a meaningful change in fortune. The severe rainfall events that brought flooding and landslides to those areas earlier in the year are expected to become less frequent in the months ahead. ESNZ noted that "areas hit by heavy rainfall are expected to shift to generally drier-than-usual conditions," and cautioned that "the prospect of below-normal winter rainfall in several regions is likely to translate to below-normal groundwater recharge, creating challenges for water-reliant sectors." That drying trend may also arrive alongside "unusually windy conditions."
ESNZ principal forecasting scientist Chris Brandolino said El Niño was "well and truly on its way".
"All the makings for a rather profound and intense event are there as well."
Canterbury and Hawke's Bay are among the regions facing a potentially tough stretch. Both areas have already recorded an unusually dry run over recent months, and Brandolino was pointed in his assessment of what prolonged shortfalls can mean. "One [dry] month, two months, not great - but you can probably deal with it. But you start getting three months, five months, six months, when the rainfall is inadequate [and] then you really start to run into problems," he said.
"You're coming off a dry winter and now you're looking at the prospect of a dry spring or dry summer ... and then you throw in really warm temperatures as you get into spring." Wind, heat, and parched ground are a dangerous combination, and Brandolino noted that such conditions could elevate fire risk, potentially sparking out-of-season fires or pulling the start of the fire season earlier than usual.
Temperature behaviour during El Niño events tends to be erratic. Brandolino described the pattern as "spiky," and pointed out that this variability plays out against the steady background warming that climate change is already delivering. "As we move through spring and summer, there's a distinct possibility that we could see some pretty hot days," he said.
His message to those with the most to lose, including farmers, horticulturists, and households dependent on tank water, is to begin preparing now rather than waiting to see how the season unfolds. He encouraged people to look back at past El Niño events or droughts and start putting a plan together while there is still time. The outlook carries some uncertainty in both directions, and Brandolino was clear that staying across updated forecasts would be essential. "It's important for people to stay on top of the forecasts, particularly for those people in a water-reliant sector."
| This story was first published on rnz.co.nz. Written by: Kate Newton of RNZ |  |
