El Niño has strengthened significantly over the past month, with scientists saying New Zealand is likely to start seeing more effects from spring as the climate pattern builds towards what could become one of the strongest in recent history.
The naturally occurring climate phenomenon, originating with the warming of ocean temperatures in the eastern and central equatorial Pacific, affected weather patterns globally.
Earth Sciences New Zealand's latest Season Climate Outlook said the tropical Pacific Ocean and atmosphere remained firmly in an El Niño state, with atmospheric indicators recording their strongest July values on record.
"We remain in its early stages; impacts on New Zealand’s weather patterns are yet to be fully felt, but are anticipated during this outlook period," the agency said.
That was expected to change throughout the next three months, as weather patterns increasingly shifted towards persistent westerly winds — a hallmark of El Niño conditions.
Scientists said there was now about a 90% chance the event would reach or surpass a "very strong" intensity during the outlook period, with peak conditions and "potential significant impacts" expected during the 2026-27 summer.
If that occurred, ESNZ said it would likely rank among the strongest El Niño events in recent history.
The top five strongest El Niño events (1972, 1982, 1991, 1997, 2015) all had sea surface temperature anomalies near or slightly above 2.5C.
Meteorologists say, given the strength of the climate event, the country will be impacted this winter. (Source: 1News)
Dry for many, wetter in lower west
The strengthening climate pattern was expected to produce very different weather across the country, ESNZ said.
Rainfall was likely to be below normal across much of the North Island, with eastern regions of both islands also expected to be drier than usual.
By contrast, the West Coast and lower South Island were forecast to receive above normal rainfall, with the risk of heavy rain and strong wind events increasing as spring progresses.
"New Zealand has experienced several heavy rain events from the north over the past year. These northerly rain events have already reduced in frequency in recent months, and this trend is expected to continue," the agency said.
"The main heavy rain threat instead is expected to shift toward the western and lower South Island."
While temperatures over August to October were expected to be near or above average across most of the country, ESNZ said that did not mean consistently warm weather.
It said cold snaps remained likely through winter and spring, while stronger westerly winds were expected to bring greater swings between warm and cool conditions.
The drier outlook was also expected to affect water supplies. ESNZ forecast soil moisture levels and river flows would be near or below normal across much of the north and east of both islands, as well as parts of the western North Island and northern South Island.
It added that reduced rainfall in several regions was likely to limit groundwater recharge, creating challenges for water-dependent sectors.
While other climate drivers, including the Indian Ocean Dipole, Southern Annular Mode and Madden-Julian Oscillation, would continue to influence New Zealand’s weather, ESNZ said El Niño was expected to become the dominant driver over the coming months.
The agency was also monitoring the possibility of a rare Southern Hemisphere sudden stratospheric warming event, which if occurred, would have the potential to influence New Zealand’s weather.
The morning's headlines in 90 seconds, including snow closes roads, Spanish police overwhelmed by a crowd of migrants, and how a car ended up inside a bus. (Source: 1News)
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