Ag Weather Forum

Sea-surface temperatures in the tropical Pacific Ocean have been rising since the turn of the calendar to 2026, after La Nina peaked in December. The current trajectory and forecasts have an El Nino taking shape over the next few weeks, which could become the strongest on record. The Climate Prediction Center (CPC) has issued an El Nino Watch as they expect ocean conditions to transition from neutral into an El Nino state over the next month.

El Nino is the positive side of the El Nino Southern Oscillation (ENSO), when sea-surface temperatures are significantly higher than normal in the tropical Pacific.

Last winter's brief La Nina, the cold side of ENSO, when below-normal sea-surface temperatures peaked at an Oceanic Nino Index (ONI) of a minus 0.6 degrees Celsius in November and December, have quickly taken a turn into neutral territory during the month of April and are heading into El Nino territory (ONI of greater than 0.5 degrees C above normal). Weekly values of the ONI have crossed the El Nino threshold on this week's update from the CPC, shown here: https://www.cpc.ncep.noaa.gov/….

However, the CPC uses a three-month average, so it will take some time for the resulting El Nino to be officially recognized. When it does, it will likely be a Super El Nino with ONI values forecast to be at or near 2.0 by the beginning of July. That is according to the American CFS model, one of the more accurate models for sea-surface temperature predictions in recent years.

The most recent model forecasts have ocean temperatures peaking out at an ONI around 3.0 in October and November, before a seasonal drop in temperatures heading into 2027. If realized, that would put the El Nino of 2026 at the top of recorded El Ninos in our short record history since 1950. The current record is from the 2015 Super El Nino, where the peak reached an ONI of 2.8, followed by 1997 at 2.4. The most recent Super El Nino in 2023 reached a peak of 2.1 C above normal. ONI values of at least 2.0 are generally regarded as a Super El Nino and are rare, occurring only six times since 1950 -- 1965, 1972, 1982, 1997, 2015 and 2023.

Current ocean temperatures below the surface tend to mirror some of the strongest events like 2015 and 1997 and are even warmer than 2023. Temperatures deep below the ocean surface are already 5 degrees C above normal at a depth between 100 and 150 meters and have been rising over the last several months. Large-scale ocean churning processes are likely to bring that water to the surface over the next several months, producing the Super El Nino.

The CFS model is known for being a little aggressive in its forecast but has had the right idea for several months now. The only questions have been: How strong would this El Nino become? When would it occur and start to influence the weather pattern? To some degree, it already has.

Another way of measuring ENSO is by using the Southern Oscillation Index (SOI), a part of ENSO that measures the difference in pressure between Tahiti and Darwin, Australia. Sometimes, these atmospheric influences precede or follow changes in sea-surface temperature and can signal whether or not the atmosphere is responding to the changes in sea-surface temperature. Indeed, monthly SOI values have fallen near and below a minus 8 (the threshold for El Nino) since April 12. Thus, the atmosphere has already started to respond to the changing sea-surface temperatures.

Those across the Americas have probably noticed the change with a cooler and stormier weather pattern in North America and the early dissipation of wet-season thunderstorms in central Brazil. Not all of this is the result of the building El Nino, but will be reinforced by it over the next several months.

History shows us developing Super El Ninos favor a milder, stormier pattern east of the Rockies in the U.S. The previous three Super El Nino years (2023, 2015 and 1997) all featured a milder summer with above-normal precipitation across a lot of the country. However, not all of these years were the same. Very cool temperatures and more widespread and average precipitation occurred in 1997; a colder pocket centered on Midwest with heavy rainfall in 2015; and more fragmented temperatures and precipitation favored some areas and avoided others in 2023.

Global impacts are starting to be felt in other areas and will expand as the months go by. Dryness and increasing drought concerns are forming in Australia and are forecast for Argentina over the next few months. The effects will increase during the Northern Hemisphere late fall and winter, including a wetter southern tier and overall warmer winter in the U.S., warmer temperatures in Japan and India, hotter and drier conditions for South Africa and Australia, and an eventual turn to wetter conditions for Argentina during their summer. Other impacts can be found on this general image here: https://www.pmel.noaa.gov/….

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John Baranick can be reached at john.baranick@dtn.com

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