Odds get longer on an El Niño winter

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It’s much less clear now than it was a few months ago whether we’ll see an El Niño winter in 2012-13, as several key indicators now suggest otherwise.

El Niño — an abnormal warming in the equatorial Pacific Ocean — is typically tied to warmer-than-normal conditions from December through February in Western Canada and the Maritimes and wet conditions across the southern U.S.

As we’ve said here before, it’s also tied to drought in crop-producing countries such as Australia and Brazil. Drought occurs in those affected countries and others at varying levels and different times during an El Niño event.

The U.S. government’s Climate Prediction Center in Maryland said this month that equatorial sea surface temperatures (SST) stayed “elevated” in September across the Pacific Ocean — which points to an El Niño event. But the margin of those anomalies dropped during that time and the anomalies in oceanic heat content — the average temperature in the upper 300 metres of the ocean — also weakened.

“Due to the recent slowdown in the development of El Niño, it is not clear whether a fully coupled El Niño will emerge,” the centre said in its diagnostic discussion on the El Niño/Southern Oscillation (ENSO) effect. “The majority of models indicate that borderline ENSO-neutral/weak El Niño conditions will continue, and about half suggest that El Niño could develop, but remain weak.”

On the other hand, variations in low-level westerly wind over the equatorial western Pacific Ocean “may portend possible strengthening of the subsurface anomalies in the coming months,” the centre said.

“The official forecast therefore favours the continuation of borderline ENSO-neutral/weak El Niño conditions into Northern Hemisphere winter 2012-13, with the possibility of strengthening during the next few months.”

The Australian government’s Bureau of Meteorology agrees with the U.S. centre, reporting Tuesday that the tropical Pacific “continued its retreat from El Niño thresholds for the second consecutive fortnight… remaining within the neutral range (neither El Niño nor La Niña).”

Given the rate of ocean cooling and “continued neutral conditions” in the atmosphere, “the chance of an El Niño developing in 2012 has reduced further over the past fortnight,” the Australian bureau said.

“However, some risk still remains while the trade winds in the western Pacific continue to be weaker than normal.”


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