The U.S. issued an "El Niño Watch" on Thursday morning, meaning that the likelihood of an El Niño event developing in the tropical Pacific Ocean during the next several months has crept above 50% for the first time. Scientists told Mashable that the Pacific Ocean appears to be primed for a potentially significant El Niño event, with changes observed in the trade winds that typically blow from east to west along and north of the equator, along with sea surface and subsurface temperature trends that are also suggestive of a developing event.
Lately, "westerly wind bursts" have helped reverse the easterly trade winds, helping to push warmer than average water from the western Pacific to the eastern Pacific, said Michelle L'Heureux, a meteorologist with the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center in Maryland, which issued the watch.
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In addition, scientists said, pulses of warm water, known as Kelvin waves, are moving below the surface from the western Pacific to the eastern tropical Pacific, and these waves can help induce El Niño conditions within about two to four months. Sometimes, though, they don't result in an El Niño, for reasons that scientists don't yet fully understand.
“We’re essentially putting people on alert that this is a potential, it is not guaranteed," L'Heureux said.
El Niño events are characterized by above average sea surface temperatures in the equatorial tropical Pacific, as well as changes in the atmospheric circulation above and around this region. Such events typically occur once every three to five years; the last event occurred in 2009-10. These events are the largest source of natural climate variability from season to season, and can profoundly reshape global weather patterns, from the West Coast of the U.S. to Australia.

Sea surface height anomalies across the Pacific Ocean on December 1, 1997. The warm water associated with El Nino raises sea surface heights. Measurements taken by the U.S. and French TOPEX/Poseidon satellite.
Image: NASA JPL.
In the U.S., El Niño tends to make itself known mainly in winter by bringing above-average rainfall to California and the southern tier of the country. L'Heureux said this event seems to be unfolding too late to help with California drought relief during the late winter and spring, as that state's dry season sets in.
“At this point, chances don’t favor the onset of El Niño in the spring,” she said.
The Pacific has been in near-neutral conditions, meaning there has been no El Niño or La Niña conditions (characterized by below-average sea surface temperatures) for about the past year and a half, L'Heureux said.
El Niño events tend to increase global average surface temperatures by adding more heat in the oceans and atmosphere. This heat comes on top of the influence of manmade global warming, and further raises the odds that 2014 — or more likely, 2015 — will set a new benchmark as the warmest year on record. A strong El Niño event in 1997-1998 vaulted global average temperatures to the top of the list, based on some data sets, although others show that 2005 was slightly warmer.

Cross-section of the tropical Pacific Ocean showing warm water at depth in the western Pacific, moving east.
Image: NOAA
L'Heureux said El Niño is linked to global average temperatures, but that doesn't mean that this year or next will definitely be a new warmest ear. “Certainly they’re significantly related. Does it guarantee a record year or not? I would say no,” she added.
Michael McPhaden, a senior scientist with NOAA's Pacific Marine Environmental Laboratory in Seattle, told Mashable that some similarities exist between the ocean and atmospheric state right now compared to observations shortly before the onset of the 1997-1998 El Niño event. This suggests that if an El Niño does occur, it could be an unusually strong one.
According to both L'Heureux and McPhaden, scientists issued this outlook without the benefit of their full compliment of available data. A network of ocean observing buoys strategically located throughout the central and eastern tropical Pacific and designed specifically for improving El Niño forecasts, is now only 40% operational, largely due to federal budget cuts. NOAA is working to repair the buoys, McPhaden said, but that may come too late for helping to predict this event.
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