El Niño and La Niña are opposite phases of the El Niño–Southern Oscillation, or ENSO: a recurring interaction between the tropical Pacific Ocean and the atmosphere. ENSO changes rainfall, winds, ocean temperatures, and the odds of certain weather patterns around the world, but it does not determine the weather at a particular place or time.
What is El Niño?
During El Niño, the central and eastern equatorial Pacific is warmer than usual and the tropical atmosphere responds. Trade winds often weaken, deep tropical convection shifts eastward, and atmospheric circulation changes can influence weather far from the Pacific.
What is La Niña?
La Niña is the cool phase. Equatorial Pacific waters are cooler than usual, trade winds are often stronger, and tropical rainfall tends to shift westward. Its typical global influence is broadly opposite to El Niño in some regions, but the strength and location of impacts vary from event to event.
How NOAA monitors ENSO
Scientists track sea surface temperatures in several Niño regions, especially Niño 3.4, while also examining subsurface heat, trade winds, cloud and rainfall patterns, and atmospheric pressure. No single weekly number establishes an ENSO event. Operational definitions require a sustained oceanic signal together with a consistent atmospheric response.
Why forecasts use probabilities
ENSO forecasts combine dynamical climate models, statistical models, observations, and expert assessment. A probability describes confidence across many plausible futures; it is not a promise. Forecast skill also changes through the year and is often lower across the Northern Hemisphere spring.
Typical impacts are not guarantees
El Niño and La Niña shift the odds of seasonal temperature and precipitation patterns, tropical cyclone activity, drought, flooding, marine heat, fisheries changes, and wildfire conditions. Local outcomes also depend on the event’s strength, timing, exact ocean pattern, other climate modes, and ordinary weather variability.
ENSO and climate change
ENSO is a natural climate cycle that existed before modern global warming. Climate change raises the background temperature on which ENSO operates and can alter the consequences of heat, rainfall, drought, sea level, and marine stress. Research continues on how ENSO’s frequency, intensity, and global influence may change.
Where to find the current assessment
For the latest official status and probabilities, use the NOAA Climate Prediction Center ENSO Diagnostic Discussion and the NOAA Climate.gov ENSO portal. This article explains the science and forecasting method rather than maintaining a separate current-status tracker.
