"Strong El Niño events like this one have classic calling cards, but surprises still happen — especially on a warming planet."
"The most potent El Niño event in almost a decade is about to exert its peak influence on North American weather. Many parts of the world are affected by El Niño, a periodic one- to two-year warming of the eastern tropical Pacific. In fact, El Niño is the biggest single shaper of Earth’s year-to-year weather variations atop human-induced climate change. And North America is one of the places where El Niño’s influence is most pronounced.
Think of El Niño as the boisterous guest around which people gather, or scatter, during the course of a holiday party. For a few months to a year or longer, unusually warm water spreads across a vast area centered on the equator, extending from South America westward. In Spanish, the phenomenon’s name refers to “the Christ child” (literally, the male infant). The name arose because of timing: Anchovy fishers had long noticed that the waters off Peru sometimes warmed, and their catches declined, during the weeks on either side of Christmas.
What kicks off El Niño is complex and not fully understood, but the strongest events tend to unfold in a familiar way. Westerly winds increase across the tropical Pacific, blunting or even reversing the usual east-to-west trade winds. In tandem, warm water is pushed eastward toward areas off the South American coast that are typically dominated by cold upwelling currents. The unusually warm sea surface and the westerly winds interact with each other, helping to stimulate rising air and heavy rain across a broad area."
Bob Henson reports for Yale Climate Connections December 12, 2023.
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