La Niña came back to the equatorial Pacific after a short break when the El Niño Southern Oscillation neutral phase was detected in the middle of the year. The event is going to last from September 2025 to December and is considered a relatively weak one, so the question arises about the extent of its impact on the weather and climate patterns all over the world. The changes in the rainfall, temperature, and sea level caused by even weak La Niña events can still be of great magnitude and can affect long-term patterns in the Americas as well as in Asia and Australia. Researchers are monitoring the temperature of the sea and the circulation of the atmosphere very attentively, as these changes determine the weather during the season, help in the preparation for the disaster, and provide the climate outlooks all over the world.
What is La Niña and why it matters
La Niña came back to the equatorial Pacific after a short break when the El Niño Southern Oscillation neutral phase was detected in the middle of the year. The event is going to last from September 2025 to December and is considered as a relatively weak one, so the question arises about the extent of its impact on the weather and climate patterns all over the world.Even the weak La Niña events can bring substantial changes to the rainfall, temperature, and sea level in the Americas, Asia, and Australia, and these changes can become long-term patterns. Researchers are closely following the sea temperature and the atmospheric circulation because these changes dictate the weather during the season, assist in disaster preparation, and provide the climate outlooks globally.
La Niña’s impact on sea level in the Pacific
Changes in ocean temperature during La Niña have an impact on sea level as well. The cooling water is denser and takes up less space, which is why the sea levels in most of the central and eastern parts of the Pacific Ocean are lower than normal. A look at the sea surface heights from space on December 1, 2025, reveals that these areas are widely covered with below-average heights, while the levels which are above the normal appear farther west.These were the readings of the Sentinel 6 Michael Freilich satellite, which were taken to the ground by scientists at NASA’s Jet Propulsion Laboratory. They have removed the seasonal cycles and the long-term trends from the data in order to be able to see the short term variations in sea level due to ENSO events more clearly. The just launched Sentinel 6B satellite, which was put into orbit in November 2025, will be able to provide even more accurate data for ENSO monitoring and climate forecasting starting in 2026.
How a weak La Niña affect weather patterns
When surface water in the equatorial Pacific is cooled, it changes the way heat and moisture are exchanged between the ocean and the atmosphere. These changes in turn can alter global wind patterns as well as mid latitude jet streams, thus influencing rainfall and temperature over the entire planet.In general, La Niña seasons are associated with drier than normal conditions in the American Southwest and wetter than normal conditions in the Pacific Northwest. But weak La Niña events are less predictable and do not necessarily adhere to these standard patterns. “The impacts of a mild La Niña or El Niño on the weather are almost impossible to predict,” said Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory.
Winter 2025–26 forecast: What to expect
Despite the fact that the present La Niña is not strong, it still has the power to affect the weather during the cold season in North America. The American Southwest could be turned into a region of dry weather, but forecasters emphasise that the results are highly uncertain.Scientists are still watching the temperatures of sea surfaces, the trade winds, and the circulation of the atmosphere, so a weak La Niña will be their main concern for climate research. Its change over the next few months will decide the extent of its influence on the weather of the region, the global climate patterns, and the seasonal forecasts all over the world.
