Source: Earth Sciences New Zealand
Outlook Summary
Regional predictions for the next three months:
- Northland, Auckland, Waikato, Bay of Plenty
- Central North Island, Taranaki, Whanganui, Manawatu, Wellington
- Gisborne, Hawke’s Bay, Wairarapa
- Tasman, Nelson, Marlborough, Buller
- West Coast, Alps and foothills, inland Otago and Southland Coastal Canterbury, east Otago.
Outlook Summary
• El Niño conditions persist in the tropical Pacific atmosphere and ocean, and by all measures the event has strengthened over the last month – including the strongest atmospheric measurements on record for July. 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.
• Air flow patterns are expected to eventually favour a prevailing westerly direction, characteristic of El Niño conditions, as the season progresses. This is expected to be more apparent from mid-spring onwards.
• Seasonal air temperatures for August – October 2026 are most likely to be near average for the east of the North Island. They are about equally likely to be near average or above average for all other New Zealand regions. This does not preclude occasional cold outbreaks, for example in early August, which are a typical aspect of late winter and spring weather patterns.
• Rainfall totals for August – October 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.
These northerly rain events have already reduced in frequency in recent months, and this trend is expected to continue. The main heavy rain threat instead is expected to shift toward the western and lower South Island.
• The likelihood of below normal rainfall in several regions is likely to translate to below normal groundwater recharge, creating challenges for water-reliant sectors.
• During August – October 2026, soil moisture levels and river flows are expected to be near normal or below normal for the east and north of both islands, the west of the North Island, and the north of the South Island. In the west of the South Island, they are expected to be near normal or above normal.
• Warmer-than-average subsurface ocean temperature anomalies have continued to strengthen and expand across the tropical Pacific, providing clear support for El Niño to intensify further and reach the very strong category in the coming months. Dynamical and statistical forecast guidance concurs, with approximately a 90% likelihood that the event will reach or exceed very strong intensity during the outlook period.
• Peak El Niño conditions are most likely to occur during the austral summer of 2026–27, with the potential for this event to have significant impacts. It is likely to develop into one of the strongest in recent history, as anticipated over the last few months (see El Niño declared, expected to intensify into one of the strongest on record).
• El Niño-related influences on regional weather patterns are expected to become more apparent later during spring as ENSO signals continue to strengthen. In New Zealand, this is expected to favour periods of active westerlies, bringing an increased risk of unusually windy conditions and notable temperature variability. How widespread and persistent these conditions become will depend on the location and strength of nearby high-pressure systems.
• Other climate drivers and intraseasonal oscillations, for example, the Indian Ocean Dipole, the Southern Annular Mode and the Madden Julian Oscillation will still contribute to New Zealand weather patterns, though El Niño is expected to be most dominant. In general, these other drivers are moving into phases which support El Niño-like impacts.
• 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 August – October 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.
Northland, Auckland, Waikato, Bay of Plenty
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are about equally likely to be above average (40% chance) or near average (45% chance).
• Rainfall totals are most likely to be below normal (50% chance).
• Soil moisture levels and river flows are about equally likely to be near normal (40% chance) or below normal (45% chance).
| Category | Temperature | Rainfall | Soil moisture | River flows |
|---|---|---|---|---|
| Above average | 40 | 15 | 15 | 15 |
| Near average | 45 | 35 | 40 | 40 |
| Below average | 15 | 50 | 45 | 45 |
Central North Island, Taranaki, Whanganui, Manawatu, Wellington
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are about equally likely to be near average (40% chance) or above average (45% chance).
• Rainfall totals are about equally likely to be below normal (40% chance) or near normal (35% chance).
• Soil moisture levels are equally likely to be near normal (45% chance) or below normal (45% chance).
• River flows are about equally likely to be near normal (45% chance) or below normal (40 – 45% chance).
| Category | Temperature | Rainfall | Soil moisture | River flows |
|---|---|---|---|---|
| Above average | 45 | 25 | 10 | 15 |
| Near average | 40 | 35 | 45 | 45 |
| Below average | 15 | 40 | 45 | 40 |
Gisborne, Hawke’s Bay, Wairarapa
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are most likely to be near average (45% chance).
• Rainfall totals are about equally likely to be below normal (45% chance) or near normal (40% chance) for the outlook period as a whole.
• Soil moisture levels and river flows are about equally likely to be near normal (45% chance) or below normal (40% chance).
| Category | Temperature | Rainfall | Soil moisture | River flows |
|---|---|---|---|---|
| Above average | 30 | 15 | 15 | 15 |
| Near average | 45 | 40 | 45 | 45 |
| Below average | 25 | 45 | 40 | 40 |
Tasman, Nelson, Marlborough, Buller
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are equally likely to be near average (40% chance) or above average (40% chance). The likelihood of increased temperature variability, including larger swings between warm and cool conditions, as well as periods of unusually windy weather, is expected to increase during spring.
• Rainfall totals are about equally likely to be below normal (40% chance) or near normal (35% chance).
• Soil moisture levels and river flows are equally likely to be near normal (45% chance) or below normal (45% chance).
| Category | Temperature | Rainfall | Soil moisture | River flows |
|---|---|---|---|---|
| Above average | 40 | 25 | 10 | 10 |
| Near average | 40 | 35 | 45 | 45 |
| Below average | 20 | 40 | 45 | 45 |
West Coast, Southern Alps and foothills, inland Otago, Southland
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are equally likely to be near average (40% chance) or above average (40% chance).
• Rainfall totals are most likely to be above normal (50% chance). The risk of active weather events, including heavy rainfall and strong winds, is forecast to increase during spring.
• Soil moisture levels are most likely to be near normal (50% chance).
• River flows are equally likely to be near normal (40% chance) or above normal (40% chance).
| Category | Temperature | Rainfall | Soil moisture | River flows |
|---|---|---|---|---|
| Above average | 40 | 50 | 40 | 40 |
| Near average | 40 | 40 | 50 | 40 |
| Below average | 20 | 10 | 10 | 20 |
Coastal Canterbury and the nearby plains, east Otago
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are about equally likely to be above average (45% chance) or near average (40% chance). The likelihood of increased temperature variability, including larger swings between warm and cool conditions, as well as periods of unusually windy weather, is expected to increase during spring.
• Rainfall totals are about equally likely to be below normal (40% chance) or near normal (35% chance).
• Soil moisture levels and river flows are about equally likely to be near normal (45% chance) or below normal (40% chance).
The full probability breakdown is:
| Category | Temperature | Rainfall | Soil moisture | River flows |
|---|---|---|---|---|
| Above average | 45 | 25 | 15 | 15 |
| Near average | 40 | 35 | 45 | 45 |
| Below average | 15 | 40 | 40 | 40 |
Graphical representation of the regional probabilities
Background
During July 2026, the Southern Oscillation Index (SOI) trended strongly negative, reaching its most negative July value on record since 1951, consistent with El Niño conditions. Based on daily observations through 29 July, the monthly SOI value was -3.4.
Sea surface temperature (SST) anomalies across the central and eastern equatorial Pacific continued to strengthen during July 2026, with positive anomalies now extending along the entire Equator east of the International Date Line. The Relative Niño 3.4 Index (RONI) averaged +1.4°C over the 30 days ending 29 July, well above the El Niño threshold. During August, the RONI is forecast to exceed +1.5°C, the threshold for a strong El Niño event. The current pattern of equatorial SST anomalies is consistent with the rapid development of a canonical El Niño event, similar to those of 1997/98 and 1982/83, in which the strongest warming is concentrated in the eastern rather than central Pacific.
During July, subsurface ocean temperatures across the equatorial Pacific were markedly above average and intensified further, particularly in the eastern Pacific (east of ~160°W). Temperature anomalies locally exceeded +8°C, occurring between depths of around 150 m (centred near 150°W) and 50 m (close to the South American coast). These subsurface anomalies are also continuing to be expressed at the surface, hence the continuing increases in the Relative Niño 3.4 Index.
Positive upper-ocean heat content anomalies (0-300 m) remain firmly established along the Equator east of the International Date Line. The magnitude of this subsurface heat reservoir is consistent with other observed indicators and with dynamical and statistical forecast guidance which together suggest that the ongoing El Niño is likely to reach very strong thresholds during the outlook period, and most likely continuing to strengthen further later in spring.
Rainfall and Convection: During July, enhanced convection and rainfall – indicated by negative outgoing longwave radiation (OLR) anomalies – was focused around the intertropical convergence zone (ITCZ) through the equatorial Pacific. Suppressed convection and rainfall – indicated by positive OLR anomalies – persisted across the Indian subcontinent and the maritime continent. This pattern of tropical rainfall anomalies was strongly consistent with an El Niño state and closely resembled a canonical El Niño configuration.
Trade winds remained dramatically weakened across the Pacific, and reversed entirely at times, characteristic of El Niño.
In summary, oceanic conditions are in an El Niño configuration, and setting the stage for further development during the outlook period, with particularly significant warmth (positive heat content anomalies) stored in the ocean along the Equator in the Pacific. These signals are only growing ever-stronger with time. Meanwhile, the atmosphere is also increasingly resembling El Niño. A fully-coupled El Niño has therefore emerged, although stronger ocean and atmospheric responses are anticipated as the event develops further.
The Relative Oceanic Niño Index forecasts indicate a 100% chance for El Niño conditions over the next three-month period (August – October 2026). The IRI/CPC forecasts also support this outlook. Further strengthening of the event is likely beyond the outlook period, and it is increasingly probable that the event will peak as one of the strongest on record.
The Southern Annular Mode (SAM) decreased from near record high values late in June, and showed a mixture of negative and positive modes throughout July. During August, the negative SAM mode is expected to be more common than it has been over the last two months, though occasional positive spells may still occur.
The Indian Ocean Dipole (IOD) value for July is neutral (+0.2°C). Forecasts from the Australian Bureau of Meteorology indicate that the IOD is likely to become positive over the next three month period, and is forecast to reach thresholds (+0.4°C) required to declare a positive IOD event during the spring season.
In the first week of July, the Madden Julian Oscillation (MJO) moved into the western Pacific, likely contributing to the low-pressure systems experienced in New Zealand. It then moved slowly eastwards, acting in concert with the El Niño. After making minimal impact in the Indian Ocean, it should emerge into the western Pacific again early in August, likely having some influence again on New Zealand weather patterns.
With the MJO in the western Pacific, it can also contribute to both oceanic and atmospheric components of El Niño strengthening further.
Local Sea Surface Temperatures (SSTs) are near average or above average around the majority of the country, and marine heatwave (MHW) conditions are continuing around much of the South Island and Tasman Sea. Forecasts from coupled ocean-atmosphere models for the next three-month period (see Sea Surface Temperature Update | Earth Sciences New Zealand | NIWA) indicate SSTs should continue to warm around the coastal waters of the country, especially around the South Island.
North NI +0.55°C
West NI +0.38°C
East NI +0.09°C
North SI +0.61°C
West SI +0.89°C
East SI +0.83°C
NZ 30-day coastal SST anomalies
(to 29 Jul 2026)
Figure 1: Latest 30 days SST anomalies to the 29 th July 2026, calculated with respect to the 1991-2020 climatological period.
* 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
Temperature
Forecast confidence for temperatures is Medium. Cold weather in early August should then trend steadily towards milder conditions, ultimately influenced by the developing westerly conditions and warm seas
surrounding the country. Periodic cold outbreaks will still occur, as is normal for spring.
Rainfall Forecast confidence for rainfall is Medium-High. El Niño influenced rainfall patterns are expected to dominate the latter parts of the outlook period. Compared with previous outlooks, confidence is higher that any uncharacteristic rain events, such as in mid-August, will not upset the overall rainfall pattern over the three month period.
Notes
1. Earth Sciences New Zealand outlooks indicate the likelihood of climate conditions being at, above, or below average for the season as a whole, relative to the 1991-2020 average. They are not ‘weather forecasts’ as it is not possible to forecast precise weather conditions three months in advance.
2. The outlooks are the result of the expert judgment of scientists and forecasters. They take into account observations of atmospheric and ocean conditions and output from global and local climate models. The presence of El Niño or La Niña conditions and the sea surface temperatures around New Zealand can be useful indicators of likely overall climate conditions for a season.
3. The outlooks state the probability for above average conditions, near average conditions, and below average conditions for rainfall, temperature, soil moisture, and river flows. When a particular probability reaches or exceeds 60%, we conclude it is “very likely”.
4. This three-way probability means that a random choice would be correct only 33 per cent (or one-third) of the time. It would be like randomly throwing a dart at a board divided into three equal parts, or casting a dice with three numbers on it.
5. Where probabilities are within 5% of one another, the term “about equally” is used.
6. All outlooks are for the three months as a whole. There will inevitably be relatively wet and dry days, and hot and cold days, within a season. 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 for the long-term mean, whereas for rainfall the “near normal” category lies between 80 per cent and 120 per cent of the long-term mean.
7. The seasonal climate outlooks are an output of Predicting climate variability and change, a scientific research programme supported through Earth Sciences New Zealand’s Strategic Science Investment
Fund.
8. The forecast confidence meter for temperature and rainfall represents the expert judgement of Earth Sciences New Zealand climate scientists. It aims to synthesize various forecast elements, such as global and local climate drivers, in order to clearly communicate forecaster confidence in how all the evidence has aligned for the seasonal outlook.