La Niña Is Here

After seven months of waiting, La Niña—the cooler sister of El Niño—finally showed up in the eastern Pacific Ocean in early December 2024. La Niña may not stick around long, though. According to NOAA, the Pacific may return to neutral conditions in spring 2025.

Part of the El Niño-Southern Oscillation (ENSO) cycle, La Niña appears when energized easterly trade winds intensify the upwelling of cooler water from the depths of the eastern tropical Pacific, causing a large-scale cooling of surface waters in the eastern and central Pacific Ocean near the equator. The stronger-than-usual trade winds also push the warm equatorial surface waters westward toward Asia and Australia. This dramatic cooling of the ocean’s surface layers affects the atmosphere by modifying the moisture content across the Pacific.

In a report published on January 9, 2025, the NOAA Climate Prediction Center confirmed that La Niña conditions were present. They measured sea surface temperatures 0.7 degrees Celsius (1.3 degrees Fahrenheit) below average in an area of the tropical Pacific, from 170° to 120° West longitude, known as the Niño 3.4 region.

The signature of La Niña is also visible in the central and eastern Pacific Ocean as areas of lower-than-average water levels. That’s because cooler water contracts, lowering sea levels. (Conversely, warmer water expands, raising them.) The map above depicts sea surface height anomalies across the central and eastern Pacific Ocean as observed on January 13, 2025. Shades of blue indicate sea levels that were lower than average, while shades of red indicate areas where the ocean stood higher than normal. Normal sea level conditions appear in white.

Data for the map were acquired by the Sentinel-6 Michael Freilich satellite and processed by scientists at NASA’s Jet Propulsion Laboratory (JPL). Note that signals related to seasonal cycles and long-term trends have been removed to highlight sea level anomalies associated with ENSO and other short-term natural phenomena.

“Although La Niña is here, it’s not a particularly strong one,” said Josh Willis, an oceanographer and Sentinel-6 Michael Freilich project scientist at JPL. Willis noted that during an especially strong La Niña in 2010-2011, temperatures in the tropical Pacific were about 1.6°C (2.9°F) below average in January 2011, compared to just 0.7°C (1.3°F) below average in January 2025. NOAA forecasts that this La Niña will remain weak and is unlikely to reach -1°C below average—the threshold at which La Niña is considered moderate in strength. Neutral conditions were expected to return in the meteorological spring, between March and May.

La Niña’s coupling with the atmosphere and ocean alters global atmospheric circulation and can cause shifts in the path of mid-latitude jet streams in ways that intensify rainfall in some regions and bring drought to others. In the western Pacific, rainfall can increase over Indonesia and Australia. Clouds and rainfall become more sporadic over the central and eastern Pacific Ocean, which can lead to dry conditions in Brazil, Argentina, and other parts of South America and wetter conditions over Central America. In North America, cooler and stormier conditions often set in across the Pacific Northwest, while weather typically becomes warmer and drier across the southern United States and northern Mexico.

ENSO adds a natural source of year-to-year variability in global temperatures. Because such a wide swath of the Pacific is cold, La Niña tends to keep a lid on the average global surface temperature. But even the cool water in the Pacific does not completely offset long-term warming trends; some of the hottest years on record have coincided with La Niña, such as in 2010 and 2020.

Source:

NASA. (2025, February 7). La Niña Is Here. Earth Observatory.