An El Niño appears to be forming along the equator off the west coast of South America in the Pacific Ocean. That could have a big effect on the weather in the United States and around the world.
For three years now, La Niña was large and in charge, but the La Niña ended, and now warmer water temperatures signal an El Niño probably is forming.
The Climate Prediction Center sees favorable chances of an El Niño and the possibility of a strong El Niño. El Niños often lead to some of the hottest years on record, including the record-high global average temperature set in 2016. That leads to fears the globe could see a new record high within the next couple of years.
El Niño’s effects can cost billions and influence storms around the world, including hurricanes. Here’s what causes El Niños and La Niñas and what they mean for our weather.
El Niño and La Niña are opposite phases of a natural climate pattern known as the El Niño ‒ Southern Oscillation. El Niño is the warm phase and La Niña is the cool phase. A third phase – neutral – produces conditions near the long-term average. Each can influence winds, surface pressures and rainfall around the world.
In a mid-May update, the Climate Prediction Center said El Niño is likely by summer and puts the chances for a strong El Niño at 55%. Climate scientists say a strong El Niño would almost certainly send temperatures soaring this year and into 2024, increasing chances for a new record high global average.
Temperatures in 2020 matched the record high set during the last El Niño in 2016, even during a La Niña. This year, ocean temperatures are already warmer than normal.
As La Niña ended, waters off South America began to warm. When the warmer than normal water reaches the Central Pacific, that’s a sign El Niño might be on the way. A responding reaction in the atmosphere is needed before an El Niño is declared.
The U.S. and North America primarily feel El Niño’s effects during the winter. They include:
- Wetter than average conditions along the Gulf Coast from Texas to Florida.
- Increased chances of above normal tornado activity in central and south Florida.
- Wetter than normal conditions in parts of California.
- Drier than normal conditions in the Ohio Valley, and potentially reduced precipitation in Washington state and Oregon during a period when the states typically receive much of their annual precipitation.
An El Niño can’t completely prevent hurricanes in the Atlantic, but it often serves to limit hurricane formation and reduce hurricane landfalls along the East Coast, giving Florida and other hurricane-prone areas a break.
During El Niño, vertical wind shear over the Atlantic hurricane region is enhanced and can tear apart the towering cloud structures that help give hurricanes their energy, high winds and rainfall.
The Walker Circulation – a large-scale, slow overturning of air in the atmosphere – is part of what allows El Niño and La Niña to have such far-reaching effects. It circulates along the equator in the tropics, driven by interaction of pressure systems over the Pacific. The jet stream that influences North America’s weather responds to where the increased precipitation and storms occur within the circulation.
During La Nina, vertical wind shear over the Atlantic decreases, and conditions that allow hurricanes to build towering clouds can happen without interference.
During El Niño, the circulation increases vertical wind shear over the Atlantic, interfering with hurricane development, while reducing vertical wind shear over the eastern Pacific.
Among effects around the globe:
- Enhanced probability of below normal precipitation for India’s monsoon.
- Eastern Australia and southern Africa see a greater probability of below normal rainfall.
- The west coast of South America and East Africa see enhanced probabilities for above normal precipitation.
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