A freight train of warm water is surging eastward in the tropical Pacific Ocean, kick-starting what is on track to be the strongest El Niño ever observed.

The latest model projections are off the charts. Literally. 

If these models prove accurate, it will set off dramatic weather impacts everywhere from California’s coast to the Arctic Ocean.

Most forecast models project Pacific Ocean temperatures to be warmer than the average by at least 3 degrees Celsius by November. For sea surface temperatures across this patch of the central Pacific, even a bump of 1 or 2 degrees Celsius is enough to reshape rainfall, storm tracks and temperatures around the world. 

Such an event would surpass the peaks of the 1997-98 and 2015-16 super El Niños, the strongest on record. In those years, ocean surface temperatures were 2.4 and 2.6 degrees Celsius above average, respectively. 

That’s not all: Several recent model projections take the anomaly even further, past 3.5 degrees Celsius and into territory that requires the standard El Niño tracking chart to be redrawn.

A month ago, atmospheric scientist Paul Roundy of the State University of New York at Albany estimated that the developing El Niño had roughly a 30% chance of becoming the strongest event in 140 years. As of this week, he has raised that estimate to 50%.

“There has been enough momentum already transferred to the ocean to make a strong El Niño event a virtual certainty,” Roundy said in an email, “but it remains a little less certain whether the event gets into record territory.”

The American multi-model ensemble, an aggregation of leading forecast systems run by the National Oceanic and Atmospheric Administration, came to a similar conclusion in its update this week. The ensemble’s peak ocean temperature forecast now sits at 3.1 degrees Celsius warmer than average for November, with the event sustained at record-strong levels through at least January.

The Pacific is already running hot at the bottom of the ocean. Below the surface, temperatures in parts of the equatorial Pacific are now more than 7 degrees Celsius above normal, more heat at this stage of an El Niño’s development than has been observed in the modern record.

Surface warmth alone can fade quickly when the trade winds — which blow east to west — rebound. But heat stored hundreds of feet below the ocean surface is harder to reverse. It is what gives a developing El Niño staying power, and it is the central reason this event looks nothing like the 2014 false start, when the warming faded by April and the anticipated El Niño didn’t arrive for another year.

Since January, a series of unusually strong westerly wind bursts has propelled warm water eastward across the Pacific Ocean basin. The most powerful, in early April, was a rare cluster of three tropical cyclones that Roundy described as potentially the strongest equatorial wind burst in more than a century.

Evidence of the strength of the coming El Niño is already showing up at the surface. As of May, the relative Niño index, NOAA’s updated measure for tracking El Niño as climate change warms the ocean, sat at +0.436 degrees Celsius. The threshold for declaring an official El Niño is +0.5 degrees Celsius, sustained for three months. 

The ocean and the atmosphere are linked; they feed each other. The warmer the Pacific gets, the more energy it dumps into the air above it, fueling deeper, more frequent thunderstorms over the central and eastern equatorial Pacific. In a normal year, the bulk of that activity sits over the western Pacific and Indonesia. In a strong El Niño, it shifts thousands of miles east.

Those thunderstorms are the heat engine that drives a chain of high- and low-pressure systems wrapping around the planet. And where they set up matters for which regions will see the greatest impacts. Move the engine, and the rest of the chain moves with it: Some regions get more rain, while others lose it. Hurricane seasons in different ocean basins run hotter or quieter than usual.

The 1982-83 and 1997-98 El Niños, two of the strongest on record, pushed those shifts to extremes. California saw double its normal winter rainfall in 1997-98 and roughly $850 million in storm damage. Peru’s fishing-reliant coastal economy took a hit on the order of 10% of GDP with each El Niño event. Eastern Pacific hurricane seasons surged. Heat and drought intensified across parts of Australia, Indonesia and southern Africa. On the flip side, the Atlantic hurricane season quieted and India’s summer monsoon weakened, reducing rainfall across a region where agriculture desperately depends on it.

A record-strength event would not necessarily replay those impacts beat for beat. But the already-high global ocean temperatures mean the conditions needed for such impacts will be in place.

Daniel Cayan, a climate researcher at the Scripps Institution of Oceanography in San Diego, said the model evidence and the ocean observations now point in the same direction.

“The warming eastern-central tropical Pacific, along with updated model forecasts, continue to indicate a strong El Niño is developing,” Cayan said.

NOAA’s Climate Prediction Center is scheduled to release its updated outlook on May 14 and is expected to raise its El Niño odds.