Strengthening El Nino likely to 'rank among largest' on record: US agency

The El Nino weather pattern picked up strength over the past month and is highly likely to "rank among the largest" ever recorded when it peaks between October and December, US forecasters said Thursday.

El Nino warms surface temperatures in the central and eastern equatorial Pacific Ocean, triggering worldwide changes in winds, atmospheric pressure and rainfall patterns, and pushing warmer overall global temperatures.

In its latest update, the US Climate Prediction Center (CPC) said there is an 81 percent chance of a "very strong" El Nino between October and December that would rank among the largest such events in the historic record going back to 1950.

"Very strong" is defined as being 2.0 degrees Celsius (3.6 degrees Fahrenheit) or more above an index value.  The CPC also put the odds at 97 percent that the event will persist through early spring 2027.

That adds to a prediction made by Tim Stockdale, an El Nino expert of the European Centre for Medium-Range Weather Forecasts, who said this week it would be "a very, very big surprise" if the event failed to be a record-breaker.

El Ninos typically have knock-on effects globally, including drier conditions and drought in Australia, along with wetter winters in East Africa and the southern United States. 

Isla Simpson, a climate scientist at the US National Center for Atmospheric Research, told AFP that "there's quite a lot of evidence from our models that global warming increases the variance of El Nino, so you get bigger El Nino events and also bigger La Nina events."

La Nina is the cooling phase of the El Nino-Southern Oscillation cycle.

Within the United States, El Nino events are typically "drought-busting" over some regions including California but drying in others. 

The connections to Europe are smaller and less certain, but there is some evidence that El Nino can increase the likelihood of cold conditions later in the winter in Northern Europe, said Simpson.

"Most likely, what we'll see are the canonical El Nino teleconnections," she said, "but in any given event, things can deviate from that just because we have all of these random uncertainties. There's weather that happens on top of these longer timescale predictable signals."

Sea surface temperatures are now 1.2C (2.2F) above average in a defined stretch of the equatorial Pacific known as the Nino 3.4 region, the CPC said.

Combined with warming waters below the surface and shifting wind and pressure patterns, the "ocean-atmosphere system reflected a strengthening El Nino."

While El Nino usually peaks between November and February, the resulting spike in temperatures typically comes later.

Compounded with human-induced climate change, the last El Nino contributed to making 2023 the second-hottest year on record and 2024 the all-time high.

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© Agence France-Presse