La Niña is a natural climate pattern in which ocean surface temperatures in the central and eastern tropical Pacific drop below normal, triggering shifts in weather around the world. It’s the cool counterpart to El Niño, and together they form a cycle called the El Niño-Southern Oscillation, or ENSO. La Niña can bring heavier rain to some regions, drought to others, and a more active Atlantic hurricane season.
How La Niña Works
Under normal conditions, trade winds blow westward across the tropical Pacific, pushing warm surface water toward Asia and Australia. During La Niña, those trade winds strengthen beyond their usual intensity, shoving even more warm water to the western Pacific. That leaves the central and eastern Pacific cooler than average, sometimes by a full degree Celsius or more.
This temperature shift rearranges atmospheric circulation over a huge area. Warm, moist air rises more vigorously over the western Pacific, fueling rain clouds there, while the cooler eastern Pacific suppresses rainfall along the equatorial coast of South America. The result is a large-scale redistribution of heat and moisture that ripples outward into weather patterns across every continent.
What Makes It Official
NOAA tracks a specific patch of ocean called the Niño 3.4 region, a band stretching from 5°N to 5°S latitude and from 120°W to 170°W longitude, roughly in the middle of the tropical Pacific. Scientists calculate a running three-month average of sea surface temperature anomalies in that zone. When that average falls at or below -0.5°C for at least five consecutive overlapping three-month periods, the event is classified as La Niña. This metric is called the Oceanic Niño Index (ONI), and it’s the standard yardstick used by climate agencies worldwide.
Weather Effects Across the United States
La Niña’s fingerprint on U.S. weather is clearest in winter. The southern tier of the country, from Southern California through Texas and across the Gulf states, tends to be warmer and drier than average. The north-central Plains, by contrast, often see colder temperatures. The Ohio Valley and the Pacific Northwest, including northern California, typically receive more precipitation than usual.
These shifts matter for water supply, agriculture, and energy demand. A drier winter in the Southwest can worsen drought conditions and raise wildfire risk heading into spring. Heavier rain and snowfall in the Pacific Northwest can boost reservoir levels but also increase the chance of flooding and landslides. Farmers in the southern Plains may face reduced soil moisture right when winter wheat needs it most.
Atlantic Hurricanes and La Niña
La Niña years are associated with busier Atlantic hurricane seasons. The mechanism comes down to wind shear, the change in wind speed and direction between lower and upper levels of the atmosphere. Hurricanes need relatively uniform winds from bottom to top to organize and intensify. During La Niña, the upper-level westerly winds over the Atlantic weaken, reducing vertical wind shear across a broad area. That gives tropical storms more room to develop into hurricanes and allows existing hurricanes to grow stronger.
Global Impacts
Outside the United States, La Niña’s most dramatic effects show up in the western Pacific and the Southern Hemisphere. Indonesia, parts of Southeast Asia, and northern Australia receive unusually heavy rainfall, often in a horseshoe-shaped pattern centered on the western Pacific. NASA satellite imagery has documented widespread flooding in northern Australia during strong La Niña events. For communities in these regions, La Niña can mean months of above-average rain, swollen rivers, and disrupted agriculture.
On the opposite side of the Pacific, countries along the western coast of South America, particularly Peru and Ecuador, tend to experience drier conditions. Fisheries off the South American coast can actually benefit, because the stronger trade winds enhance upwelling of cold, nutrient-rich water from the deep ocean, supporting marine food chains.
Effects on Global Crop Yields
La Niña’s reach extends into global food production. Research published in Agricultural Systems found that La Niña reduced average global yields for rice by 2.1%, maize by 1.5%, and soybeans by 1.3%. Soybeans were the most variable crop, with yield swings as large as 5.9% in some La Niña years. Wheat bucked the trend, gaining about 1.0% on average, likely because many major wheat-growing regions benefit from La Niña’s cooler or wetter conditions.
These percentages sound small, but applied to global production volumes they translate into millions of tons of food. For commodity markets, even a 1-2% shortfall in maize or soy can tighten supply and push prices higher, with the effects felt most acutely in import-dependent countries.
How Long La Niña Lasts
La Niña events typically develop between June and November, peak during the Northern Hemisphere winter, and can persist for one to three years. Multi-year events are more common with La Niña than with El Niño. Some episodes weaken briefly before re-intensifying the following fall, a pattern sometimes called a “double-dip” La Niña.
As of early 2025, La Niña conditions were in place, with NOAA’s Climate Prediction Center forecasting a transition to ENSO-neutral by February through April 2026 (60% probability). ENSO-neutral conditions were then expected to persist through at least the Northern Hemisphere summer of 2026.
La Niña vs. El Niño
La Niña and El Niño are opposite phases of the same cycle. El Niño warms the central and eastern Pacific, weakens trade winds, and generally brings wetter conditions to the southern United States while suppressing Atlantic hurricane activity. La Niña cools the same ocean region, strengthens trade winds, and does roughly the reverse. Between the two, there are neutral periods when Pacific temperatures hover near the long-term average and neither pattern dominates.
The full ENSO cycle, from one El Niño through neutral and La Niña phases and back again, typically runs two to seven years, though the timing is irregular. No two events are identical; the strength of the temperature anomaly, its precise location along the equator, and interactions with other climate patterns all shape how each event plays out in regional weather.