Sea surface temperatures in the tropical Pacific have resumed warming, possibly signaling a coming onset of El Nino (NWS)

For the second straight month, forecasters at the National Weather Service have nudged down the likelihood of El Nino event occurring by the winter.

Examining recent El Nino forecasts, you could jump to the conclusion El Nino prospects are dying a slow death. In May, the National Weather Service said there was an 80 percent chance of an El Nino by winter, but in August it reduced those chances to 65 percent. Now they’re down to 60-65 percent.

But forecasters say odds for an El Nino event are still in our favor and point to auspicious indicators.

For one, ocean temperatures in the tropical Pacific are warming; a critical development since El Nino events are defined by warmer than normal ocean waters in that region. After ocean temperatures warmed this spring – fueling El Nino speculation – the trend reversed this summer. But ocean warming has resumed, says Michelle L’Heureux, climate analyst at the National Weather Service.

“The weekly Nino-3.4 index has increased over the last 3 weeks: from 0.0C to 0.3C to 0.4C,” L’Heureux said in an email.  Thus, the Pacific is nearing the cusp of meeting El Nino criteria which requires the index to warm to 0.5C, remain at that level for at least one month, and be complemented by an El Nino signal in the atmosphere.

Models forecasts, on average, continue to project an El Nino event will occur.

Model forecast for El Nino.El Nino is achieved when the index shown meets/passes the 0.5C threshold for at least one month. (IRI/CPC)

El Nino skeptics may point to the fact model forecasts have predicted less Pacific ocean warming since June when it forecast the Nino-3.4 index to be 0.9C by the October-November-December period. Now, the model average for that timeframe is 0.6C – just above the El Nino threshold.

“Yes, fizzling is a possible outcome,” says L’Heureux says. “We’re not betting on it, but it could happen.”

Seemingly off the table is the prospect for a strong El Nino. The overwhelming majority of model forecasts suggest the El Nino will be a weak one.

An El Nino event, if it occurs and depending on its strength, could help relieve the California drought while favoring a snowy winter in the Mid-Atlantic. While not completely formed as of the moment, it is thought to already be increasing Pacific hurricane activity and decreasing Atlantic hurricane activity in its fledgling state.

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