After a several-month hiatus, La Niña returned to the equatorial Pacific Ocean in September 2025 and has continued into December. However, this occurrence of El Niño’s cooler counterpart is relatively weak, and its influence on weather and climate over the next several months remains to be seen.
Part of the El Niño-Southern Oscillation (ENSO) cycle, La Niña develops when strengthened easterly trade winds intensify the upwelling of cold, deep water in the eastern tropical Pacific. This process cools large swaths of the eastern and central equatorial Pacific while simultaneously pushing warm surface waters westward toward Asia and Australia. In a report published on December 11, the NOAA Climate Prediction Center confirmed that below-average sea surface temperatures associated with La Niña conditions were present and likely to continue for another month or two.
The shifting wind patterns and the movement of heat within the ocean have a direct impact on sea level. Because cooler water is denser and occupies less volume than warm water, sea levels in the central and eastern Pacific drop during La Niña events. The map above shows sea surface height observed on December 1, 2025. Shades of blue indicate below-normal sea levels, shades of red show above-normal levels, and white represents near-normal conditions.
Data for the map were acquired by the Sentinel-6 Michael Freilich satellite and processed by scientists at NASA’s Jet Propulsion Laboratory (JPL). Signals related to seasonal cycles and long-term trends …