WeatherARC Blog

What is El Niño?

El Niño is an oscillation in the ocean-atmosphere system in the tropical Pacific.¹ During El Niño the trade winds relax causing the warm water to pile up in the Eastern Pacific. This relaxation of the trade winds also tends to push much of the rainfall, normally occurring in the Western Pacific, eastward closer to South America. With the trade winds being such a big part of the global atmospheric circulation pattern, changes in the trade winds can bring about changes in the atmosphere circulation pattern elsewhere around the globe.

During non-El Niño or non-La Niña conditions the trade winds blow east to west across the tropical Pacific. They cause the warm water normally present in that region of the Pacific to pile up in the Western Pacific in turn causing there to be a higher sea surface in the Western Pacific than in the Eastern Pacific. This wind pattern pushes the warm water westward away from the South American coast. As a result we see an upwelling of cooler water in the Eastern Pacific.

What are some of the effects of El Niño across the globe?

During the Northern Hemisphere Summer¹:
- Wetter in parts of the Central Rockies, within the contiguous U.S.
- Drier in Southern Central America down into Northern South America
- Drier in the East Indies down through Eastern Australia
- Drier in Central India

During the Northern Hemisphere Winter¹:
- Wetter in the Southeast U.S.
- Wetter around Ethiopia and Sudan
- Wetter in parts of Argentina and Uruguay
- Drier in the East Indies
- Drier from Tanzania south to South Africa and east to Madagascar
- Drier in northeast South America
- Warmer in the Northeast U.S. up into Canada
- Warmer in Southern Alaska down into Canada
- Warmer in North and South Korea east into Japan

What is the current status of El Niño?

We are currently experiencing a weak to moderate El Niño and with it forecast to strength into a moderate and possibly strong El Niño by winter.

What does this mean for us here in the U.S.?

The El Niño will continue to make conditions in the Atlantic Ocean increasingly unfavorable for tropical development. So we will likely see fewer tropical storms for the remainder of the hurricane season.

The U.S. is generally not impacted as strongly by El Niño until the winter time, so much of the impacts of El Niño will not be felt in the U.S. until the winter time. The southeastern U.S. will likely see a wetter than usual winter this year and it will likely be warmer than usual in the much of the western U.S.

(Forecast courtesy of the Climate Prediction Center)

¹http://www.pmel.noaa.gov/tao/elnino/el-nino-story.html