La Nina events arise when stronger-than-normal easterly trade winds enhance the upwelling of cold, deep water in the eastern tropical Pacific, lowering sea surface temperatures across large areas of the eastern and central equatorial basin. At the same time, these winds drive warmer surface waters westward toward Asia and Australia, reinforcing temperature contrasts across the Pacific.
In an update issued on December 11, 2025, the NOAA Climate Prediction Center reported that La Nina conditions, defined by below-average sea surface temperatures in the equatorial Pacific, were present and likely to continue for at least another month or two. These temperature anomalies are a key metric used by forecasters to track ENSO phases and assess their likely climate impacts.
Changes in ocean temperature during La Nina directly affect sea level because cooler water is denser and occupies less volume than warmer water. As a result, sea levels typically fall in the central and eastern Pacific during La Nina episodes and rise in regions where warmer water accumulates, especially farther west.
A recent map of sea surface height from December 1, 2025, highlights these contrasts, showing a band of lower-than-normal sea level as shades of blue across the central equatorial Pacific and higher-than-normal levels in red elsewhere, with white indicating near-average conditions. By removing signals associated with seasonal cycles and long-term trends, the visualization isolates short-term changes linked to ENSO and other natural variability.
The Sentinel-6 Michael Freilich satellite collected the sea surface height data used in the map, and scientists at NASAs Jet Propulsion Laboratory processed the observations. The mission provides high-precision measurements of sea level across the globe, supporting studies of ENSO dynamics and other ocean processes.
Sentinel-6 Michael Freilich now has a successor in orbit, Sentinel-6B, which launched in November 2025 and is expected to begin contributing data for ENSO research and forecasting in 2026. Together, the satellites extend a multi-decade record of satellite altimetry that underpins both climate studies and operational ocean monitoring.
Cooling of equatorial surface waters during La Nina modifies the exchange of heat and moisture between the ocean and atmosphere, which can reshape global atmospheric circulation. This coupling often shifts mid-latitude jet streams, increasing rainfall in some regions while favoring drier conditions and drought in others.
Historically, La Nina winters tend to bring reduced rainfall to the American Southwest and wetter conditions to the Pacific Northwest. However, the current event is weak, and such mild ENSO phases do not always produce consistent regional patterns.
When La Nina or El Nino is weak, the associated climate signatures can be difficult to anticipate. Project scientist Josh Willis of JPL described the resulting weather signals as "notoriously difficult to predict," underscoring the uncertainty around seasonal outlooks during mild ENSO events.
"It still has the potential to tilt our winter toward the dry side in the American Southwest," Willis said. "But it's never a guarantee, especially with a mild event like this one."
NASA Earth Observatory image by Lauren Dauphin, using modified Copernicus Sentinel data (2025) processed by the European Space Agency and further processed by Josh Willis and Kevin Marlis/NASA/JPL-Caltech. Story by Kathryn Hansen.
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