On 1 July 2025, NIWA merged with GNS Science to become Earth Sciences New Zealand.

Island Climate Update

A monthly summary of the climate in the tropical South Pacific islands, with an outlook for the coming months.

August-October 2025 Island Climate Update

ENSO-neutral conditions remain in place, and there is a 60% chance that ENSO-neutral conditions will continue during August-October 2025, followed by a 55% chance that ENSO-neutral will remain in place during September-November.

As of 21 July 2025, the 30-day NINO3.4 Index (in the central equatorial Pacific) was +0.02˚C, in the neutral range. The 30-day relative Niño 3.4 Index (RONI) was -0.28˚C, reflective of the central equatorial Pacific being cooler than the average of the global tropics and on the La Niña side of neutral.

The Southern Oscillation Index (SOI) was on the La Niña side of the neutral range during May-July (+0.7), while the July value was also +0.7 (on the La Niña side of the neutral range). 

Temperatures in the subsurface equatorial Pacific are generally above average in the western part of the basin with cooler than average temperatures developing in the east. Should these cooler temperatures in the east reach the surface in the coming months, it could push ENSO in a La Niña direction.

Upper oceanic heat content continues to indicate ENSO-neutral conditions.

The South Pacific Convergence Zone (SPCZ) was located close to its climatological normal position during July.

During August-October, model guidance favours an enhancement in convective forcing over the western Pacific and Melanesia, collocated with the warmest sea surface temperatures. This may lead to enhanced rainfall for island groups such as Palau and Papua New Guinea east to Fiji and Tonga.

However, drier than normal conditions are likely to occur for most island groups along and north of the equator, including the Federated States of Micronesia, the Marshall Islands, Nauru, Kiribati, Tuvalu, Tokelau, and parts of French Polynesia (see pages 6-7 for more information).

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Additional resources

Additional regional and country situation summary and forecast information can be obtained below. Current rainfall accumulation status and other derived summary information are updated on a daily basis (with a 2-day lag), with seasonal forecast information updated once per month.

About the Island Climate Update

NIWA is the Network co-lead for the WMO RA V Regional Climate Centre Node on Long Range Forecast and consortium member for nodes on Climate Monitoring, Operational Data Services and Training.

Development and production of the ICU is supported by NIWA Strategic Science Investment Funding under contract PRAS2301. The Island Climate Update bulletin and associated video and products are prepared as soon as possible at the start of each month. Delays in data availability occasionally arise. While every effort is made to verify the data, NIWA does not guarantee the accuracy and reliability of the analysis and forecast information presented and accepts no liability for any losses incurred through the use of this bulletin and its contents. The contents of this bulletin and all associated products produced by the Island Climate Update may be freely disseminated provided the source is acknowledged.

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View past monthly Island Climate Update issues (2001 to present) here Island Climate Update | NIWA

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