Positive Indian Ocean Dipole Could Influence European Winter, but No Guarantees

The Australian Bureau of Meteorology confirms that a positive Indian Ocean Dipole episode has been underway since the start of September 2026, alongside a rarely intense El Niño. According to several studies, this tropical thermal balance can bend the Atlantic jet stream. What remains to be measured is what it actually changes for Europe’s winter.

With an index of +0.69 °C by the end of October 2026, the Indian Ocean Dipole clearly crosses its positive phase threshold

The Indian Ocean Dipole, or IOD, compares the sea surface temperature in the western part of the basin, off East Africa, with that in the eastern part, south of Indonesia. When the west warms more, the index becomes positive. Thus, the phase flips when the east dominates.

In its bulletin dated October 27, 2026, the Bureau of Meteorology notes an index of +0.69 °C for the week ending October 25. The value has remained above the +0.4 °C threshold for seven consecutive weeks. Moreover, all models examined forecast a return to neutrality around December, the start of the Australian summer.

This episode coincides with a strong El Niño as judged by the same organization. However, the separate effects of the two oceans on Europe remain difficult to disentangle.

A 2020 Met Office study links the positive dipole of 2019 to Northern Europe’s very mild and wet winter

The hypothesis rests on work by Steven Hardiman and colleagues at the Met Office, published in 2020 in Atmospheric Science Letters. The team dissected the winter of 2019-2020, marked by a strongly positive North Atlantic Oscillation (NAO). Yet, a very intense positive dipole had set in just beforehand.

Using composite analyses and modeling experiments, the authors conclude that the IOD was a key driver of this positive NAO. It drives toward Northern Europe a mild and humid air. Moreover, the simulated rainfall matches what was observed in the United Kingdom.

Two atmospheric pathways, via the troposphere and via the polar vortex, carry the signal to the North Atlantic

The proposed mechanism relies on two routes. First, enhanced convection over the western Indian Ocean triggers a train of Rossby waves, which travels across the Pacific and then the Atlantic. Second, a second pathway passes through the Aleutian region and the stratospheric polar vortex.

These routes resemble those already documented for El Niño. Consequently, the North Atlantic jet stream can shift and strengthen, promoting the passage of depressions across northern Europe. However, the study focuses on a single winter, and the broader link remains probabilistic.

Météo-France estimates a 70% probability of a quarter warmer than normal, also aided by climate change

In its bulletin dated October 29, 2026, Météo-France favors for November, December, and January a pattern of low pressures over the nearby Atlantic. The probability of a warmer-than-normal quarter reaches 70% across France and Corsica. Additionally, wetter conditions are deemed likely in the northern half of the country.

The agency attributes this scenario to the anticipated circulation and to the trend linked to climate change. The dipole is therefore only one ingredient among others. Importantly, a seasonal forecast describes a likely average over the three months.

Colder episodes remain possible, Météo-France notes. Accordingly, a positive IOD does not guarantee a mild winter; it merely increases the odds. The expected return to neutrality in December could also limit the duration of its influence on the season.