Outlook Summary

• Very strong El Niño conditions are firmly established in the tropical Pacific and have intensified further in October. Forecasts indicate the event may reach its peak during the outlook period (November 2026 to January 2027). As a result, El Niño is expected to remain the primary driver of New Zealand's climate patterns over the coming three months.
• A westerly-quarter circulation pattern is expected to prevail for much of the season, consistent with the influence of a very strong El Niño. Higher than normal pressure is favoured to the north of New Zealand and lower than normal pressure to the south.
• A mix of northwesterly, westerly, and southwesterly airflows is expected during the season, with periodic low-pressure systems bringing more active and unsettled weather, particularly to the South Island.
• Despite some uncertainty in the balance of these circulation patterns, all forecast scenarios favour enhanced westerly-quarter flow overall. As a result, confidence is relatively high for a drier-than-normal season in the east of the North Island and a wetter-than-normal season in the far south and west of the South Island.
• Temperatures for November 2026 to January 2027 are most likely to be above average across the North Island and the east of the South Island. Near average or above average temperatures are forecast for the north of the South Island, while near average temperatures are most likely in the west of the South Island. Temperatures are expected to be more variable than usual, with periods of warmth interspersed with cooler spells. Spells of unusually high temperatures are expected to be most frequent and intense on the eastern sides of both islands.
• Rainfall totals for November 2026 to January 2027 are most likely to be below normal in the north and east of the North Island and above normal in the west of the South Island. Confidence is relatively high in these outcomes, particularly for the dry signal in the east of the North Island and the wet signal in the southwest of the South Island, which are supported across most forecast scenarios. In the east of the South Island, near normal or below normal rainfall totals are about equally likely. Near normal rainfall is most likely in the west of the North Island and the north of the South Island. However, forecast probabilities are more evenly distributed in these two regions, reflecting greater uncertainty in the seasonal rainfall outcome.
• Soil moisture, river flows, and lake storage levels remain generally healthy across the South Island, although conditions have become somewhat drier in some regions and snow storage has recently dropped below typical levels for the time of year. In contrast, below normal soil moisture and river flows are evident across parts of the North Island. The east and north of the North Island are particularly likely to experience reduced rainfall, more frequent dry spells, and continued drying of soils and vegetation, likely creating challenges for water-dependent sectors.
• Soil moisture levels and river flows are most likely to be below normal in the east and north of the North Island, while near normal or above normal conditions are favoured in the west of the South Island. Near normal or below normal soil moisture levels and river flows are expected for the remaining regions of New Zealand.

• The Relative Oceanic Niño Index (RONI) has already surpassed the peak values recorded during the 1997/98 El Niño and is rapidly approaching the maximum reached during the 2015/16 event (see El Niño 2026: What you need to know for real-time tracking), despite those events not reaching their peak intensity until much later in the year. Coupled with the unprecedented rate of warming observed since January 2026, this suggests the current El Niño is likely to rank among the strongest on record and may ultimately become the strongest observed in the instrumental era.
• The outlook period (November 2026-January 2027) coincides with the beginning of the Southwest Pacific tropical cyclone season. The Southwest Pacific Tropical Cyclone Outlook indicates normal to above normal tropical cyclone activity for the basin as a whole, while the risk for northern New Zealand is considered near normal. Historically, strong El Niño events tend to shift tropical cyclone activity eastward across the Southwest Pacific, increasing activity in the central and eastern parts of the basin relative to normal.

Regional predictions for November 2026 – January 2027

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.

 

During October, subsurface ocean temperatures in the eastern equatorial Pacific, east of the International Date Line, continued to warm. Temperature anomalies now locally exceed +11°C at depths of approximately 50-100 m east of 120°W. This reservoir of exceptionally warm water continues to feed the surface warming signal, supporting further increases in the RONI. Meanwhile, cooler-than-average subsurface temperatures persist across the western equatorial Pacific. This pronounced east-west contrast is characteristic of very strong eastern-Pacific El Niño events and has emerged remarkably rapidly during 2026, consistent with the exceptional pace of development observed at the surface.

Accordingly, and consistent with conditions observed last month, positive upper-ocean heat content anomalies (0-300 m) remain firmly established along the Equator east of the International Date Line. The magnitude and persistence of this subsurface heat reservoir are consistent with other observed oceanic and atmospheric indicators, as well as dynamical and statistical forecast guidance, all of which point to further strengthening of El Niño during the outlook period.

Rainfall and Convection: Negative OLR anomalies continued across the central and eastern equatorial Pacific during October, signalling enhanced tropical convection and rainfall east of the International Date Line. Conversely, positive OLR anomalies persisted over the Maritime Continent, indicating suppressed convective activity. Together, these anomalies reflect a marked eastward displacement of tropical convection that is characteristic of a very strong eastern-Pacific El Niño.

Atmospheric circulation across the tropical Pacific remained strongly altered from normal during October. The usual easterly trade winds were considerably reduced in strength, with occasional reversals to westerly flow indicative of a mature and strongly coupled El Niño event.

In summary, very strong (“super”) El Niño conditions remain firmly established across the tropical Pacific and have continued to intensify, consistent with earlier forecasts. The event is expected to strengthen further and likely reach its peak during the November 2026 to January 2027 outlook period. A substantial reservoir of anomalous warmth persists below the surface in the eastern equatorial Pacific ocean, providing ongoing support for the event's development. Oceanic indicators have strengthened markedly over recent months, while atmospheric indicators remain strongly aligned with El Niño conditions. Trade winds, tropical convection, and the Southern Oscillation Index all exhibit a robust El Niño signature, increasing confidence that El Niño will remain the dominant driver of New Zealand's climate during the coming season.

The Relative Oceanic Niño Index forecasts indicate a 100% chance of very strong El Niño conditions persisting during November 2026 – January 2027. This assessment is consistent with forecasts from the IRI/CPC. Forecasts from the Multi-Model Ensemble system used by ESNZ broadly favour two plausible evolution pathways. In one, El Niño reaches maximum intensity during November before weakening relatively quickly; in the other, the event continues to strengthen into December or January before entering a more gradual decline. In both cases, peak RONI values are projected to exceed those observed during historically strong El Niño events. This El Niño is likely to rank among the strongest on record and may ultimately become the strongest observed in the instrumental era.

Looking farther ahead, some long-range forecast models suggest a possible shift towards La Niña conditions from winter 2027 onward. Earth Sciences New Zealand will continue to monitor the evolution of these signals in the coming months. Forecasts of El Niño – Southern Oscillation (ENSO) phase transitions tend to exhibit enhanced skill when initialised during exceptionally strong events such as the current El Niño.

A significant ozone hole persists over Antarctica and is associated with a stronger-than-normal stratospheric polar vortex, a configuration that can favour positive Southern Annular Mode (SAM) conditions at the surface. While the SAM was predominantly positive in late September and early October, it has since returned to near-average values. Although SAM-related influences will continue to be monitored, the exceptionally strong and well-coupled El Niño is expected to be the primary driver of atmospheric circulation across the New Zealand region during the outlook period.

The Indian Ocean Dipole (IOD) remained in a positive phase during October, with a 30-day index value of +0.76°C as of 26 October. Forecast guidance from the Australian Bureau of Meteorology indicates further strengthening, with the event expected to reach peak intensity during November. The current state of the Indian Ocean is consistent with the broader tropical climate pattern associated with El Niño. While sea surface temperatures continue to show a pronounced east-west gradient across the tropical Indian Ocean and trade winds remain stronger than average, the cooler-than-normal conditions typically observed near Indonesia during positive IOD events have yet to fully develop.

The Madden-Julian Oscillation (MJO) exerted little influence on tropical climate patterns during October. Any intra-seasonal variability was overshadowed by the much stronger large-scale signals associated with the mature El Niño event and the positive phase of the IOD.

Local sea surface temperatures (SSTs) remained near average to above average around most of New Zealand during October and generally increased compared with September. Recent warming has resulted in strong marine heatwave conditions developing along parts of the east coast of the South Island and in the Nelson-Tasman region, although these are not expected to persist. Looking ahead, coupled ocean-atmosphere model forecasts for the next three months (see Sea Surface Temperature Update | Earth Sciences New Zealand | NIWA) indicate a gradual cooling trend around much of New Zealand, with SSTs expected to become less anomalously warm through the outlook period.

[1]The Relative Oceanic Niño 3.4 Index (RONI) is a modern way of measuring oceanic El Niño and La Niña that is complementary to traditional oceanic indices. While traditional oceanic indices like the Niño 3.4 Index monitor SSTs in one region, the RONI compares the average SST in the central equatorial Pacific with the average SST across the global tropics. Since tropical rainfall patterns respond to changes in ocean temperatures, this new relative index can help forecasters better determine if the equatorial Pacific is warmer or cooler than the rest of the global tropics, which has become more challenging to discern as seas warm because of climate change.

Forecast Confidence