There is a 60% chance that La Niña will develop by January 2025. Tropical Pacific trade winds will continue to push the ocean in a La Niña-like direction during December.
As of 19 November, the traditional 30-day Niño 1+2 Index anomaly was -0.12˚C, within the neutral range. The 30-day NINO3.4 Index anomaly (in the central equatorial Pacific) was -0.22˚C, also in the neutral range.
An alternative measure of central Pacific SSTs, called the relative oceanic Niño Index, has had an average anomaly of –0.84˚C over the last 30 days (to 19 November) and is more aligned with La Niña-like oceanic conditions.
The Southern Oscillation Index (SOI) was in the neutral range during September-November (+0.1), while the November value was -0.1 (in the neutral range), a decrease since last month.
The subsurface equatorial Pacific continues to be 2˚C to 4˚C cooler than average just below the surface in the east of the basin.
Above average upper oceanic heat content continues in western parts of the Pacific basin. The West Pacific Warm Pool is continuing to become more unusually warm, which is also reflective of the potential development of La Niña.
The South Pacific Convergence Zone was located slightly south of its climatological normal position during November.
During December-February, model guidance favours an enhancement in convective forcing over the western Pacific and Maritime Continent, consistent with a developing La Niña. This may lead to enhanced rainfall for some countries such as Palau, Federated States of Micronesia, Marshall Islands, and southern Papua New Guinea east to Fiji (based on the decile precipitation forecast for December and December-February; see pages 6-7 for more information).
Tropical cyclone season continues through April 2025. While no activity is forecast in the short-term, it is important to remain vigilant and prepared as tropical cyclone season is now underway.
