There is a 50% chance that La Niña will develop during January-March 2025, although La Niña-like weather patterns are likely even if atmospheric and oceanic indicators do not meet traditional La Niña thresholds. Strong tropical Pacific trade winds have pushed the ocean in a La Niña-like direction during December.
As of 16 December, the 30-day NINO3.4 Index (in the central equatorial Pacific) was -0.27˚C, in the neutral range. The 30-day NINO1+2 Index (in the eastern Pacific) was +0.28˚C, also within the neutral range. The 30-day relative Niño 3.4 Index (RONI) was -0.75˚C, reflective of the central equatorial Pacific being significantly cooler than the average of the global tropics.
The Southern Oscillation Index (SOI) was on the La Niña side of the neutral range during October-December (+0.7), while the December value was +1.0 (on the La Niña threshold), a significant increase since last month.
The subsurface equatorial Pacific is 1˚C to 3˚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, which is also reflective of the potential development of La Niña.
The South Pacific Convergence Zone (SPCZ) was located slightly south of its climatological normal position during December.
During January-March, model guidance favours an enhancement in convective forcing over the western Pacific and Maritime Continent, consistent with La Niña-like patterns. This may lead to enhanced rainfall for some island groups such as Palau, Guam, Northern Marianas, Federated States of Micronesia, Marshall Islands, and the Solomon Islands east to Niue (see pages 6-7 for more information).
Tropical cyclone season continues through April 2025. While no activity is forecast in the short-term, tropical cyclone chances may increase from mid-January as a pulse of the Madden-Julian Oscillation (MJO) is expected to move through the western Pacific Ocean.
