During El Niño, unusually warm surface water occupies more of the central and eastern tropical Pacific and trade winds weaken. During La Niña, those waters are cooler than average and trade winds strengthen. The atmosphere and ocean change together.
Three things to know
- System
- ENSO
- The El Niño–Southern Oscillation couples tropical ocean and atmosphere.
- Irregular cycle
- ~2–7 years
- Events recur irregularly rather than on a fixed calendar.
- Reach
- Global
- Atmospheric teleconnections shift weather far beyond the Pacific.
When wind and warm water reinforce each other
Trade winds normally help pile warm surface water in the western tropical Pacific and promote upwelling of cooler water in the east. When winds and sea-surface temperatures shift, each can reinforce the other, changing rainfall and pressure patterns across the basin.
La Niña is not simply El Niño backward
La Niña tends to strengthen the normal east–west contrast, while El Niño weakens it. Their effects vary by event, season and region. A forecast therefore describes changed probabilities—not a guarantee of one outcome for every town.
Why ocean heat changes weather
The tropical Pacific is a vast source of heat and moisture to the atmosphere. Moving its warmest water changes where air rises, clouds form and high-altitude winds flow. Those changes can influence drought, flood and storm patterns around the world.
What people usually ask
Is every warm Pacific year El Niño?
No. NOAA uses sustained temperature anomalies plus atmospheric indicators in a defined tropical-Pacific region.
Does La Niña mean global cooling everywhere?
No. It changes global averages and regional probabilities, but local conditions vary.
Here’s where the answer came from
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