The long-established Pacific Ocean atmospheric indicator of El Nino or La Nina, the Southern Oscillation Index (SOI), shows notable signs of El Nino strength as of early June. The SOI values for June 2 were calculated at -14.79 for the 30-day average; -6.56 for the 90-day average; and -27.13 for the daily index reading.

The Southern Oscillation is the accompanying atmospheric circulation to the warming or cooling phases of the Pacific Ocean. The Southern Oscillation Index tracks the comparison between barometer readings at Darwin, Australia, and the island of Tahiti. Sustained negative values of the SOI lower than −7 often indicate El Nino episodes.

The early June SOI values are comparable to the three recent strong El Nino years identified by DTN's weather risk assessment team of 1997, 2015 and 2023. In fact, this year's SOI value on June 2 was stronger in the El Nino category than on the same date in 2015 and 2023. In those years, the SOI values were +6.40 (2015) and -17.93 (2023). Only June 2, 1997, had a more intense SOI value in the direction of El Nino than this year at -48.70.

The latest SOI value calculated for the month of May also shows how 2026 is holding its own in this feature compared to the identified three strong El Nino years. The May 2026 SOI value was calculated at -13.22. That value compares favorably with 1997's May SOI of -18.65; 2015's -13.11 SOI for May; and an SOI value of -15.26 for May in 2023.

It will be interesting to track the ongoing evolution of this developing El Nino in relation to the three previous years of strong El Nino formation. Looking at the history of the three benchmark El Nino events, we find that each year tracked a little differently than the others. In 2023, the May monthly SOI value of -15.26 was also the strongest El Nino-related value for that event. 1997 and 2015 had another level of intensity still to come. In 1997, the peak monthly SOI for El Nino came in June at -24.30; and in 2015, the peak El Nino-related SOI value did not occur until October, when the SOI measured -21.30 for the most intense monthly value in that El Nino occurrence.

The daily SOI calculations can also produce numerical "noise" but are still worth noting as a general indicator of the overall Pacific Ocean state of affairs. And in the three identified El Nino analog years, the most-intense daily SOI readings had these details: 2015 had a value of -49.77 on Oct. 3; 2023 had a strongest El Nino reading of -64.63 on May 24. And the 1997 El Nino logged a strongest-intensity daily value of -85.72 on May 31. It will be interesting to see if 2026's daily SOI numbers approach these values in the three identified strong El Nino years.

Note: SOI values in this article are from records kept by the Australia Bureau of Meteorology, and are available at: https://www.longpaddock.qld.gov.au/….

For more on El Nino's effect on Australian crops see: https://www.dtnpf.com/….

Bryce Anderson can be reached at bryce.anderson@dtn.com

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