It’s a subtle shift, but not a meaningless one: NOAA announced today the odds of an El Niño developing this summer are greater than 50 percent. In its last El Niño outlook, it placed the odds at exactly 50/50.

“The model predictions of ENSO [El Niño Southern Oscillation] for this summer and beyond are indicating an increased likelihood of El Niño this year compared with last month,” NOAA writes in its monthly discussion.

Computer models generally forecast sea surface temperature in the tropical Pacific to warm to levels over 0.5 degree C above normal this summer or fall, which would signal El Niño conditions (IRI/NOAA)

An El Niño event, characterized by warmer than normal ocean temperatures in the equatorial Pacific, can have significant effects on weather all over the world – including increased risk of drought in Australia, decreased Atlantic hurricane activity, increased winter precipitation in the Southern U.S., and, sometimes, increased rainfall in California. Frequently, El Niño events  tend to elevate the global temperature and have been associated with the warmest years on record.

Although NOAA predicts just over a 50/50 chance of El Niño  by the summer, it says the probabilities increase after that.

“There’s a 65% likelihood that El Niño will develop by later in the fall,” Mike Halpert, director of NOAA’s Climate Prediction Center, tells USAToday.

Australia’s Bureau of Meteorology is even more confident than NOAA that El Niño is on the way. On Monday, it determined the chance of El Niño in the next four months is at least 70 percent. From its announcement:

…surface and sub-surface ocean temperatures have warmed considerably in recent weeks, consistent with a state of rapid transition [towards El Niño]. International climate models surveyed by the Bureau indicate continued warming of the central Pacific Ocean in coming months. Most models predict sea surface temperatures will reach El Niño thresholds during the coming winter [northern hemisphere summer] season.

NOAA figure of ocean heat beneath the sea surface shows warm water pooling in the tropical Pacific, a possible El Niño precursor (NOAA)

While NOAA’s outlook leans toward El Niño development, it cautions the devil is in the details and that models may not have them quite right.

“Despite this greater model consensus, there remains considerable uncertainty as to when El Niño will develop and how strong it may become,” NOAA writes. “This uncertainty is amplified by the inherently lower forecast skill of the models for forecasts made in the spring.”

NOAA’s latest El Niño outlook follows a wave of press coverage and chatter in meteorological circles suggesting the developing El Niño has potential to be a strong one. See these three press accounts, for example:

In his ImageGeo blog, University of Colorado’s Tom Yulsman points to an independent NOAA analysis that favors a moderate to strong El Niño:

“…in his monthly analysis, Klaus Wolter of NOAA’s Earth Systems Research Laboratory noted that the evolution of conditions over the past four months suggest that a strong El Niño may well be on the way,” Yulsman writes.

Cliff Mass, a professor of meteorology at the University of Washingtion, is taking a more cautious approach. He writes: “…it does look we will be in at least a weak El Nino next winter, but stay tuned for more details and more confident forecasts during mid-summer.”