El Niño set to hit this winter with forecast to be dry in NZ’s north and east; wet in west

A forecast of anomalous rising air (cold colours) and sinking air (warm colours) from one of the global climate models used by Earth Sciences NZ. The Earth Sciences NZ visualisation based on data from ECMWF SEAS5 shows the globe in March 2026 and what’s forecast in September 2026, with New Zealand pictured in the lower centre.

El Niño and La Niña are the two phases of the El Niño–Southern Oscillation (ENSO), a natural climate cycle driven by ocean temperatures and atmospheric pressure across the tropical Pacific, he said.

During El Niño, warmer-than-average ocean temperatures develop in the central and eastern Pacific, weakening the trade winds, and shifting tropical rainfall towards the central and eastern Pacific.

El Niño’s impacts extended downstream of the circulation changes in the tropics, shaping New Zealand’s weather, Tunster said.

While ENSO only accounted for some of the country’s weather variability, it played a key part in influencing where areas of high pressure tended to sit over New Zealand.

What does it mean for our weather?

The forecast atmospheric response from the El Niño could strengthen the tendency for high-pressure systems to be anchored over the Australian continent during winter, resulting in a southwesterly flow over New Zealand, Tunster said.

“This could bring increased rainfall to Southland, parts of Otago, and western-facing areas, primarily of the South Island, but reduced rainfall for much of the remainder of the country.

“Dryness could become an issue as spring approaches, for areas that see a reduction in their normal winter rainfall such as the east of both islands, or the upper North Island.”

There’s a dry weather risk for eastern and northern New Zealand as a “strong” El Nino weather pattern looks likely from winter on, weather experts say. Pictured are stock gathered around a water trough during a dry spell north of Auckland in 2020. Photo / Jason Oxenham

Although southwesterly wind patterns could be associated with cold winters, a colder than usual winter across the entire nation appeared unlikely at this stage, he said.

“We could see occasional cold snaps, lasting a few days at a time – except in inland parts of the South Island where the cold air can linger for longer periods.

“Or a colder-than-average month within an otherwise near-average season.”

More rain may not be welcomed by some, with several wet weather events taking lives and damaging homes and public infrastructure this year. Pictured is a flooded street in Wellington’s Stokes Valley in February. Photo / Billy Paine

Dramatic impacts on globally important, large-scale weather systems looked likely, including the Indian monsoon and the North Pacific storm track, Tunster said.

“Given the projected strength of this event, it will be very surprising if New Zealand doesn’t feel some impacts.

“However, surprises are always possible.”