As of September 2026, every major forecasting centre projects a very strong El Niño through the coming winter. Two additional months of ocean observations have strengthened the outlook since the June briefing. Sea-surface temperatures in the equatorial Pacific do not directly determine harvest outcomes. Their effects vary by crop, region and stage of development, so a single ocean index is insufficient for assessing commodity risk. This update explains Treefera's method and refreshes the first-mile assessment using the latest ocean, weather and crop data.
The index question
The standard measure of ENSO strength is the Oceanic Niño Index (ONI): a rolling three-month average temperature anomaly within a fixed box drawn over the central Pacific, compared to a 30-year baseline. As the whole tropical ocean warms, that baseline drifts further from today's temperatures, and the ONI now reads consistently hot. The US Climate Prediction Center's preferred measure is the Relative ONI (RONI), which subtracts the warming shared across the entire tropical belt and retains only the relative contrast between the Niño 3.4 box and its neighbours, the gradient that actually reorganises the atmosphere.
Using the forecast inputs available in June, the adjustment materially affected the ranking. After removing the effect of shared tropical warming, the event ranked as the sixth strongest since 1950: comparable with major events such as 1997-98 and 2015-16, but not unprecedented. ONI indicated the largest event on record, while RONI placed it among the six strongest historical events. The choice of index therefore affected how trading and procurement teams assessed the season.
The September composite incorporates two additional months of ocean observations. These inputs place Treefera's multi-model RONI composite at +3.24°C for the November-January peak, ahead of every past event since 1950, including 1982-83 (+2.36°C), 1997-98 (+2.28°C) and 2015-16 (+2.25°C). On the latest inputs, both ONI and Treefera's RONI composite indicate a record event.
A material difference remains between Treefera's composite and NOAA's official RONI outlook. NOAA's 13 August outlook puts the November-January median at +2.23°C, which would rank the event second since 1950, behind only 1982-83. The difference reflects methodology as well as timing. Treefera's composite blends the full multi-model ensemble (CFSv2, NMME, C3S and CanSIPS) and gives greater weight to the upper end of a widening spread. NOAA's product is a more conservative institutional consensus. The resulting ranking depends both on the index selected and on the forecast methodology used.
For reference: ONI ranks the current forecast first since 1950. NOAA's official RONI outlook of 13 August 2026, at +2.23°C, ranks it second behind 1982-83. Treefera's multi-model RONI composite of 7 September 2026, at +3.24°C, ranks it first. The June composite, based on the inputs available at that point, ranked it sixth.
Both readings indicate a major event at or near the top of the historical record. The regional mechanisms described below may therefore be operating under conditions outside, or at the upper bound of, the observed historical range.
From index to analogue
For each commodity, Treefera matches the forecast RONI value to the closest historical analogues: years in which the Pacific state most closely resembled the current forecast trajectory. We then reconstruct the weather experienced by each growing region during those years. Both the mechanism and magnitude are relevant. Drought in West Africa during an El Niño year does not imply comparable risk in Brazil; similarly, stress during Vietnam's dry season can coincide with anomalous moisture in the Southern Plains.
The June analysis used the six-to-seven closest analogues since 1980 to describe the distribution of outcomes under the forecast available at that point. The September composite, incorporating the latest inputs, now sits close to a full degree above the strongest analogue year on record. The analogue composites in this piece and the companion analyses on coffee, cocoa and US grains should therefore be read as a lower bound on potential regional impact rather than a central estimate. The new inputs also widen the range of plausible commodity outcomes.
How the translation works
Footprint weighting underpins every analysis. A regional temperature or rainfall anomaly matters only in proportion to where the crop actually grows. A moisture deficit centred on the eastern Corn Belt carries different weight if Iowa is dry than if it falls on Kansas or Indiana. Every climate signal Treefera processes is weighted by the spatial distribution of the crop canopy, derived from Treefera's own production area maps, not by administrative boundaries or simple geographic averages.
Biological window alignment determines which crops the ENSO signal can reach. ENSO's atmospheric consequences peak from November through January and decline by spring. A crop whose critical period — flowering, pollination or grain fill — overlaps that window is exposed, while one whose critical period falls outside it has little direct exposure. Southern Plains winter wheat is sown in October and fills grain through the following spring, so its growing cycle spans the ENSO peak. Using the current underlying dataset, production in the region tracks the preceding-winter RONI at r = +0.52. US corn pollinates in mid-July, months after the El Niño signal has declined. The crops therefore have different ENSO exposures because of their calendars. The September US grains analysis extends this framework with weather and yield observations collected through August.
Satellite observations reduce the delay between field conditions and published data. Treefera's Greenprint Weather Pipeline continuously derives crop-stress indices, canopy health metrics and soil moisture profiles at multiple depths from ERA5 reanalysis and satellite observations. These measures can be available weeks before official surveys are conducted or published. In spring 2026, Treefera quantified a 63.8 millimetre precipitation deficit across the hard red winter wheat belt in April, the deepest in the 45-year ERA5 record and two months before the May WASDE reflected the shock. By August, Treefera estimated national winter wheat yield at 39.84 bu/ac, compared with USDA's estimate of 47.05, with the difference concentrated in hard red winter wheat. In 2022, Treefera's corn yield signal indicated 175.8 bushels per acre five weeks before USDA revised its WASDE estimate towards the NASS final of 173.4.
The accuracy record
The models' performance can be measured against published outcomes. Over 2020-2024, Treefera's US corn yield model achieved a mean absolute error of 2.07 bushels per acre, compared with 3.33 for USDA WASDE during the pre-survey period: a 38% reduction in error. The Ghanaian cocoa production-area detection model records a season-end F1 score of 0.932. Treefera has also tracked US corn yield to within 1% of the NASS final several weeks before market consensus formed, with verified uncertainty estimates.
Why this matters for 2026-27
Treefera's composite now places the 2026-27 RONI forecast first since 1950, while NOAA's official outlook places it second. Both classify it as a major event. Three companion pieces published this September refresh the crop-level analysis using new first-mile inputs. The structural risks identified in June remain the starting point; observations collected through August provide a more current view of their regional distribution and development.
For Brazilian arabica, the June analysis identified lower frost exposure under El Niño and elevated pre-existing climate stress. The frost watch closed in July without an event, while wetter conditions subsequently reduced stress as the crop moved through harvest. For robusta, the structural water vulnerability identified in Đắk Lắk remains relevant; August observations add current stress readings for Gia Lai and Brazil's conilon belt, where heat and evaporative demand are more prominent. In West African cocoa, new-season data show lower drought stress than in 2024-25, while forward indicators for the opening 2026-27 crop point to tighter supply conditions. In US grains, observations through August show continued deterioration in winter wheat following the record spring moisture deficit, while timely rainfall reduced the sub-surface moisture pressure identified in corn. Treefera's latest yield estimates incorporate those new seasonal inputs. Across all three analyses, the September view extends the June baseline with refreshed first-mile data rather than replacing the earlier assessment.
For traders and risk managers, the lag between observed field conditions and official reporting can create mispricing. A basin-scale "record El Niño" headline provides limited differentiation across commodity markets. The more relevant assessment identifies the crop, region and biological stage exposed to the signal.
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