El Niño Likely: 70 Percent Chance by Summer

The 10-day average sea-surface height centered on May 2, 1997 (left), and May 3, 2014. (Shades of red and orange indicate warmer water that's above normal sea level; blue-green shows below-average sea level and temperatures; and white indicates normal sea-level conditions.)

(Image credit: NASA Earth Observatory, TOPEX/Poseidon satellite (1997), Ocean Surface Topography Mission/Jason 2 satellite (2014).)

Time to place your bets: The chance of an El Niño developing this year continues to rise, forecasters with the National Atmospheric and Oceanic Administration said today (June 5).

NOAA's Climate Prediction Center (CPC) puts the odds of an El Niño at 70 percent this month and 80 percent during the fall and winter. But it's too soon to officially declare an El Niño, because the ocean and atmosphere are sending mixed signals, the CPC said in its monthly El Niño outlook, released today.

First, a quick definition: An El Niño is part of a natural climate cycle called the El Niño Southern Oscillation. The cycle swings between warmer water (an El Niño) to colder water (La Niña) in the eastern Pacific Ocean. [How El Niño Causes Wild Weather All Over the Globe (Infographic)]

During a potential El Niño year, scientists watch for unusually warm water in the eastern Pacific, along with weakening easterly trade winds, which usually block warm water from flowing toward the eastern Pacific.

Currently, wind and rainfall patterns don't quite match with a maturing El Niño. As warmer water moves eastward, so do the clouds and thunderstorms associated with it. Tropical rainfall patterns still haven't shifted away from Indonesia as expected during an El Niño year, the CPC said. Trade winds haven't slowed down yet, either, though the winds usually don't weaken until fall during an El Niño.

However, even though the atmosphere isn't showing strong signs of an El Niño, ocean temperatures have crossed the threshold that forecasters typically use to define an El Niño, the CPC said. Its latest measurements peg temperature anomalies between 1.1 and 2.9 degrees Fahrenheit (0.6 and 1.6 degrees Celsius), above the 0.9 F (0.5 C) threshold.

The missing atmospheric response to this warm water makes for a tricky forecast. The ocean is clearly heading toward an El Niño, but the atmosphere says "conditions neutral," the CPC said.

The CPC said significant uncertainty accompanies their outlook for strength: forecasters aren't sure whether this year's El Niño will be weak or strong. For now, models call for a moderate-size event.

But forecasters remain "just as confident that El Niño is likely to emerge," the CPC said.

El Niño is known for moving atmospheric moisture around the globe, causing snowy winters in the Northeast and wet winters in the Southwest. In turn, drought often strikes in Southeast Asia and Australia.

The next El Niño update will be released on July 10.

Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on Live Science.

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Becky Oskin covers Earth science, climate change and space, as well as general science topics. Becky was a science reporter at Live Science and The Pasadena Star-News; she has freelanced for New Scientist and the American Institute of Physics. She earned a master's degree in geology from Caltech, a bachelor's degree from Washington State University, and a graduate certificate in science writing from the University of California, Santa Cruz.