Conditions in the tropical Pacific are approaching La Niña, and therefore a La Niña Alert is now in effect. There is a 70% chance that La Niña conditions will develop during November 2025-January 2026, with a 55% chance that La Niña conditions will continue during December 2025-
February 2026.
As of 18 October 2025, the 30-day NINO3.4 Index (in the central equatorial Pacific) was -0.47˚C, in the neutral range. The 30-day relative Niño 3.4 Index (RONI) was -0.82˚C, indicating La Niña conditions and reflective of the central equatorial Pacific being cooler than the average of the
global tropics.
The Southern Oscillation Index (SOI) was on the La Niña side of the neutral range during August-October (+0.4), while the October value was +0.8 (in the La Niña range). Subsurface ocean temperatures in the equatorial Pacific remain above average in the western part of the basin with cooler than average temperatures in the east. Notably cooler than average temperatures are currently located in the eastern equatorial Pacific at depths of 50-200 metres. These cool water temperatures indicate a tropical Pacific on the brink of La Niña.
During November, a pulse of the Madden-Julian Oscillation (MJO) is predicted to move across the Pacific. This will result in an enhancement in convective activity and rainfall.
During November-January, model guidance favours an enhancement in convective forcing over the western Pacific and parts of Melanesia consistent with La Niña and colocated with the warmest sea surface temperatures. This may lead to enhanced rainfall for island groups such as Palau, western Federated States of Micronesia, and Papua New Guinea east to parts of French Polynesia. Conversely, drier than normal conditions are likely to occur for most island groups near the equator, including parts of the Marshall Islands, Nauru, Kiribati, Tuvalu, Tokelau,
northern Cook Islands, and northern French Polynesia (see pages 6-7 for more information).
