Seasonal Climate Outlook June - August 2025

Outlook summary

Neutral El Niño – Southern Oscillation (ENSO) conditions remain present in the tropical Pacific.  

Residual signals indicative of weak La Niña conditions persist, and occasional La Niña-like atmospheric patterns may still emerge over the next three months

International guidance indicates about a 70% chance for the tropical Pacific to remain in an ENSO-neutral state over the outlook period.

For New Zealand, higher than normal atmospheric pressure is expected to the east of the country, leading to north-easterly flow anomalies that may shift to a more north-westerly direction towards the end of the three-month period.

Low pressure systems forming north of the country are still expected to affect New Zealand and may lead to heightened risks for heavy rainfall events.

Seasonal air temperatures are expected to be above average across all New Zealand regions for this winter season. Thus, while cold snaps and frost will occur, they are expected to be less frequent than usual.

Sea surface temperatures (SSTs) remain well above average around most of New Zealand, except in offshore areas east of the North Island. In May, coastal SST anomalies ranged from +0.39°C to +1.47°C. Large regions offshore are currently experiencing Marine Heatwave (MHW) conditions. Global climate models suggest that SSTs in the New Zealand region are likely to stay above average over the next three months, although the intensity of the anomalies may ease. Monitor the SST update for updates.

June – August rainfall totals are expected to be above normal for the north of the North Island and near normal for the east of the South Island. For all remaining regions of the country, rainfall is forecast to be near normal or above normal. Sub-seasonal, or monthly, projections of rainfall and dryness are updated daily through the NIWA35 forecast.

During June – August 2025, near normal soil moisture levels and river flows are expected for all regions of the North Island, while near normal or above normal soil moisture levels and river flows are forecast for the South Island.

Regional predictions for June – August 2025

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

• Temperatures are very likely to be above average (65% chance).   
• Rainfall totals are most likely to be above normal (45% chance) for June – August 2025 as a whole, with occasional heavy rain events expected.
• Soil moisture levels and river flows are most likely (45-50% chance) to be near normal.

	Temperature	Rainfall	Soil moisture	River flows
Above average	65	45	25	35
Near average	20	35	50	45
Below average	15	20	25	20

 Central North Island, Taranaki, Whanganui, Manawatu, Wellington

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are very likely to be above average (60% chance).   
• Rainfall totals are about equally likely to be above normal (40% chance) or near normal (35% chance).
• Soil moisture levels and river flows are most likely (40-45% chance) to be near normal.

	Temperature	Rainfall	Soil moisture	River flows
Above average	60	40	35	30
Near average	25	35	45	40
Below average	15	25	20	30

Gisborne, Hawke’s Bay, Wairarapa

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are most likely to be above average (45% chance).   
• Rainfall totals are about equally likely to be near normal (40% chance) or above normal (35% chance). 
• Soil moisture levels and river flows are most likely (45% chance) to be near normal.

	Temperature	Rainfall	Soil moisture	River flows
Above average	45	35	35	30
Near average	35	40	45	45
Below average	20	25	20	25

Tasman, Nelson, Marlborough, Buller

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are very likely to be above average (60% chance).
• Rainfall totals are equally likely to be above normal (40% chance) or near normal (35% chance).
• Soil moisture levels and river flows are equally likely to be near normal (40% chance) or above normal (40% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	60	40	40	40
Near average	25	35	40	40
Below average	15	25	20	20

West Coast, Southern Alps and foothills, inland Otago, Southland

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are very likely to be above average (60% chance).
• Rainfall totals are about equally likely to be near normal (40% chance) or above normal (35% chance).
• Soil moisture levels and river flows are about equally likely to be near normal (40% chance) or above normal (35% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	60	35	35	35
Near average	25	40	40	40
Below average	15	25	25	25

Coastal Canterbury and the nearby plains, east Otago

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are very likely to be above average (60% chance).
• Rainfall totals are most likely to be in the near normal range (40% chance).
• Soil moisture levels and river flows are about equally likely to be near normal (40-45% chance) or above normal (35-40% chance).

The full probability breakdown is:

	Temperature	Rainfall	Soil moisture	River flows
Above average	60	30	40	35
Near average	25	40	45	40
Below average	15	30	15	25

In May 2025, upper-ocean heat content (temperature anomalies in the upper 300 metres of the ocean) remained above average across the western tropical Pacific, particularly west of approximately 170°W. Anomalies exceeding +2°C persisted south of the Equator, from the Maritime Continent to the International Dateline, near the latitude of the Solomon Islands. East of the Dateline, while isolated areas north and south of the Equator exhibited negative anomalies, heat content along the Equator itself was generally near average. This distribution is consistent with the tropical Pacific Ocean having transitioned away from La Niña conditions.

In the subsurface equatorial Pacific, ocean temperatures remained significantly above average (anomalies > +3°C) between approximately 100- and 200-metres depth west of 170°W. Over the past week, these warm anomalies have expanded eastward and risen in the water column, with above-average temperatures now observed below roughly 50 metres depth west of about 130°W. In contrast, the central and eastern Pacific show limited cooler anomalies, with only a single isolated pocket of below-average temperatures near 50 metres depth off the South American coast.

Taken together, these indicators suggest that the tropical Pacific ocean has largely transitioned away from La Niña conditions observed earlier this year. Notably, the previously prominent east–west gradient in heat content and subsurface temperature anomalies has diminished.

Based on the dynamical and statistical models monitored by NIWA, ENSO-Neutral conditions remain the most likely outcome (73% chance) over the next three-month period (June – August 2025). However, intermittent weak La Niña-like atmospheric patterns may still occur over the winter season. For the remainder of the calendar year, ENSO-Neutral conditions are expected to persist. The guidance available however suggests the possibility for La Niña conditions to return by summer 2025 – 2026.

The Southern Annular Mode (SAM) was mostly positive during the month of May (85% of days positive) and the monthly average anomaly was +0.5 std. A positive SAM index is typically associated with higher pressure than normal over New Zealand. Over the next two weeks, the SAM is forecast to become temporarily negative and then return to slightly positive values.

The Indian Ocean Dipole (IOD) is currently in the neutral range, with the average anomaly for the month of May* 2025 being +0.36^oC. The guidance from the Australian Bureau of Meteorology is for the IOD to remain in the neutral range until at least July after which it is forecast to become negative.

During May 2025, intra-seasonal convective activity associated with the Madden-Julian-Oscillation (MJO) was generally weak, despite a temporary increase in MJO amplitude over the Maritime Continent mid-May. The MJO is likely to remain weak or indiscernible in the coming two-week period.

Sea surface temperatures (SSTs) remain significantly higher than average around much of New Zealand. The exception is off the east coast of the North Island, where SSTs are currently near average. Marine Heatwave (MHW) conditions – defined as five or more consecutive days with SSTs above the 90^th percentile – are ongoing along the west and southeast coasts of the South Island, as well as the west and northeast coasts of the North Island. SST forecasts for the June – August 2025 period suggest a slight weakening of these anomalies. However, above-average ocean temperatures are expected to persist around New Zealand through the winter season.

RONI: The Relative Oceanic Niño 3.4 Index (RONI) is a modern way of measuring oceanic El Niño and La Niña that is complementary to oceanic traditional 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