The PDO sat at -1.84 in August 2026, having been negative in every month since January 2020, while El Niño strengthened toward a possible record. The research on this does not support a simple answer. A negative PDO argues for weaker North American teleconnections and for stronger Australian and western North Pacific ones, and the 2023-24 event that everyone reaches for as the cautionary case turns out not to be a PDO story at all.
Two things are true about the Pacific right now and they do not usually sit together. El Niño is strengthening toward what CPC gives a 75 percent chance of being a historic event in October to December. And the Pacific Decadal Oscillation, measured by NCEI from the North Pacific SST field, stood at -1.84 in August 2026. It has now been negative in every month since January 2020.
A strong El Niño developing under a deeply negative PDO has one close modern precedent, 2023-24, and that event is remembered for teleconnections that did not show up. So the question in the headline is a fair one. The answer the literature actually supports is more interesting than yes or no: the PDO does not turn El Niño up or down. It changes where and how reliably El Niño expresses itself, and the sign of that effect is different in different parts of the world.
The PDO is often described as a background state that El Niño happens on top of. That framing does not survive contact with the index itself. The PDO's spatial pattern includes a tropically forced component, which means a strong El Niño tends to push the PDO positive rather than the other way round. The record shows it plainly.
| Event | Aug | Sep | Oct | Nov | Dec | Late-winter value |
|---|---|---|---|---|---|---|
| 1982-83 | -0.08 | +0.51 | +0.15 | -0.60 | +0.16 | +1.73 (Mar 1983) |
| 1997-98 | +2.27 | +1.80 | +1.78 | +1.48 | +0.99 | +1.52 (Feb 1998) |
| 2015-16 | +0.98 | +0.97 | +0.84 | +0.17 | +0.29 | +1.56 (Mar 2016) |
| 2023-24 | -2.48 | -2.99 | -2.23 | -1.79 | -1.66 | -1.54 (Mar 2024) |
| 2026-27 | -1.84 | — | — | — | — | pending |
This event is already showing it. The PDO bottomed at -4.21 in July 2025, before El Niño developed, and has climbed to -1.84 by August 2026. It is still deeply negative, but the direction of travel over the past year is up, which is what the tropical forcing argument predicts.
In 1982 the PDO was near zero through the autumn, ranging from -0.60 to +0.51, and only went strongly positive the following March. In 2015 it was modestly positive in August and September and faded to +0.17 by November before climbing to +1.56 in March 2016. The one event that was strongly positive throughout the autumn was 1997-98.
This matters for how the "canonical strong El Niño" is remembered. The idea that big events come with a positive PDO is built mostly on 1997-98, plus the late-winter flips of 1983 and 2016. It is not a rule that held from the start of those events. What is genuinely unusual about 2026 is not that the PDO is negative in September. It is that the PDO is at -1.84 in September, which is deep, and that the only comparable case is 2023-24.
The strongest result here comes from Maher, Kay and Capotondi (2022, Environmental Research Letters), who used five single-model initial-condition large ensembles to isolate the modulation. Their finding is that "a positive PDO enhances winter and spring El Niño temperature and precipitation teleconnections and diminishes La Niña teleconnections." The mechanism runs through the Aleutian Low and the Pacific jet: with a positive PDO the Aleutian Low deepens further and the jet strengthens, which sharpens warm advection into Alaska and northwestern Canada and intensifies the storm track into California. A negative PDO does less of this.
Two caveats belong with that result, and the authors put them there themselves. The effect is probabilistic, not deterministic: PDO phase shifts the likelihood of an anomaly, it does not determine one, and the spread across individual events is large. And the result is about the extratropical expression of El Niño, not about the strength of the tropical event.
Beniche and colleagues (2024, Scientific Reports) looked specifically at extreme El Niño events and found something that cuts the other way. Using observations and ensemble simulations with the CNRM-CM6.1 atmospheric model, they report that only extreme El Niño events, naming 1982-83, 1997-98 and 2015-16, display a statistically significant eastward shift relative to the familiar Pacific-North American pattern. Moderate events, both central-Pacific and eastern-Pacific flavours, and La Niña events do not.
The condition for that distinct pattern is specific, and it is worth reading closely: it emerges "when equatorial SST anomalies are both eastward-shifted and sufficiently large to exceed the deep atmospheric convection threshold over most of the eastern Pacific." When that happens, the paper reports wet conditions over the Western United States at greater than 0.5 standard deviations with 74 percent likelihood, and warm anomalies over Canada and the northern United States at greater than 0.5 standard deviations with 71 percent likelihood, "with more consistency across events and ensemble members than for any other El Niño or La Niña type."
So the extreme-event literature says the most reproducible North American teleconnection of all is the one that belongs to events shaped exactly like this one. As of CPC's 10 September discussion, the 2026 event satisfies both stated conditions: the SST anomalies are eastward-shifted, with August monthly relative values of +3.4°C in Niño 1+2 against +1.8°C in Niño 3.4, and CPC reports enhanced convection and rainfall persisting "from the central to the eastern Pacific." That is the convection threshold being met in the east, observed rather than modelled.
These two results are not in contradiction. Maher and colleagues describe a modulation that applies across El Niño events generally. Beniche and colleagues describe a regime that only extreme events enter. A reasonable reading is that a negative PDO argues for a weaker North American signal, an extreme eastward-shifted event argues for a stronger and more reproducible one, and 2026 has both features at once. Anyone claiming confidence about the North American winter on the strength of the PDO alone is leaving out half of the relevant literature.
2023-24 is the obvious cautionary case: the fourth strongest event since 1979, and a Pacific-North American pattern that barely showed up. It is tempting to file that under "negative PDO," since the PDO was at -2.99 that September.
The paper that examined it does not reach that conclusion. Zhang and colleagues (2025, Communications Earth & Environment) attribute the weak extratropical response to anomalously weak tropical Pacific rainfall changes, which they report were about a third as strong as in previous super El Niño events, and they trace that suppression to unprecedented warming in the tropical Indian and Atlantic Oceans in 2023 acting against the Pacific signal. The PDO and the North Pacific background state are not part of their explanation.
That is a useful correction, and it points at a better diagnostic than the PDO index. The thing to watch is not the North Pacific. It is whether tropical Pacific convection actually relocates. Teleconnections are driven by the atmospheric heating that comes with rainfall, not by the SST anomaly itself. In 2023-24 the SST anomaly was large and the rainfall response was not, and the teleconnections followed the rainfall. In 2026 CPC is currently reporting enhanced convection from the central to the eastern Pacific and suppressed convection over Indonesia, which is the response 2023-24 lacked.
The most common error in PDO commentary is to assume the modulation has one sign everywhere. It does not.