Earth Sciences New Zealand Outlook: July – September 2026

02 Jul 2026, 10:40 by Earth Sciences New Zealand · SCOOP

Outlook Summary

• El Niño conditions have now been reached in the tropical Pacific atmosphere and ocean, according to criteria assessed by Earth Sciences New Zealand. The event remains in its early stages; impacts on New Zealand’s weather patterns are yet to be fully felt but are anticipated later in the year.

• Air flow patterns are expected to tend towards a westerly flow anomaly, characteristic of El Niño conditions, as the season progresses. Transitional behaviour from June is expected to extend into at least part of July, with clear westerly-quarter flow anomalies becoming more apparent later in the forecast period.

• Seasonal air temperatures for July – September 2026 are about equally likely to be near average or above average for all New Zealand regions. Although cold snaps and frosts are expected to occur.

• Rainfall totals for July – September 2026 are about equally likely to be near normal or below normal for the north and east of the South Island, and the east of the North Island. Rainfall is most likely to be below normal for the remainder of the North Island. Meanwhile, rainfall is most likely to be above normal for the west of the South Island.

• New Zealand has experienced several heavy rain events from the north over the past year. In the coming months, these northerly rain events are expected to become less frequent, with the heavy rain threat shifting toward the western and lower South Island.

• 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.

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• During July – September 2026, soil moisture levels and river flows are expected to be near normal or below normal for the east and north of both islands, and the west of the North Island. In the west of the South Island, they are expected to be near normal.

• Warmer than average subsurface ocean temperature anomalies have continued to intensify and expand in the tropical Pacific – this means that a significant El Niño event is increasingly likely.

• There is about an 80% chance for El Niño to reach or exceed strong intensity over the outlook period (July – September 2026).

• ElNiño–related influences on regional weather patterns are expected to become more apparent later in the season as ENSO signals strengthen.

• In a New Zealand context, later this winter and especially into spring, this is expected to translate to periods favouring active weather including unusually windy conditions, along with notable temperature variability.

• Peak ElNiño conditions are expected to occur during the austral summer of 2026–27, with the potential for this event to have significant impacts (see: https://earthsciences.nz/news/el-nino-declared-expected-to-intensify-into-one-of-the strongest-on-record)

• Sudden Stratospheric Warmings (SSW) are historically rare in the Southern Hemisphere, but in recent years have become more common. Predictability is limited, but there is justification for enhanced monitoring over the coming weeks. If an SSW does occur, its impacts on New Zealand weather patterns can be delayed by a month or more.

• Out-of-season Southwest Pacific tropical cyclones (July–October) are extremely rare. When they do occur, it is almost always under El Niño conditions. This remote risk does not currently factor into New Zealand's current Seasonal Climate Outlook, although active monitoring remains in place.

Regional predictions for July – September 2026

The tables below show the probabilities (or percent chances) for each of three categories: above average, near average, and below average. In the absence of any forecast guidance there would be an equal likelihood (33% chance) of the outcome for any of the three categories. Forecast information from local and global guidance models is used to indicate the deviation from equal chance that is expected for the coming three-month period. All outlooks are for the three months averaged as a whole. During these three months, there will inevitably be relatively wet and dry periods, as well as hot and cold periods. The exact range in temperature and rainfall within each of the three categories varies with location and season. However, as a guide, the “near average” or middle category for the temperature predictions includes deviations up to ±0.5°C relative to the

long-term mean, whereas for rainfall the “near normal” category lies between 80 percent and 120 percent of the long-term (1991-2020) mean.