Australia's BOM Confirms El Niño Phase as Positive Indian Ocean Dipole Begins to Stir

Australia's Bureau of Meteorology says the El Niño–Southern Oscillation "is now in an El Niño phase," with its preferred ocean index running at more than double the event threshold — and a second, potentially reinforcing climate driver beginning to stir in the Indian Ocean.

In its latest monitoring, covering data to the week ending 26 July, the Bureau reported its relative Niño3.4 index at +1.94°C, far beyond the +0.80°C threshold it uses to characterise El Niño conditions. The index warmed by roughly 0.5°C over the preceding fortnight — a rapid climb consistent with the intensification being reported by agencies across the Pacific.

Why "relative" matters

The Bureau's index deserves a word of explanation, because it is deliberately different from the raw Niño 3.4 anomalies quoted by NOAA and others. BOM's relative Niño3.4 index subtracts the effect of background ocean warming, measuring how much the central equatorial Pacific stands out against the rest of the warming tropics. In a world of record ocean heat, an unadjusted anomaly partly reflects global warming rather than El Niño itself; the relative index isolates the ENSO signal. That a warming-adjusted index still reads +1.94°C in July underlines that this is a genuinely large event, not an artefact of a hot baseline.

One further note on how the Bureau communicates: BOM retired its former "ENSO Outlook" dial — the Watch and Alert ladder familiar from past events — in December 2025. Its assessments now come through fortnightly Climate Driver Updates rather than a graded alert level.

The Indian Ocean joins in

The same update carried the first sign of a companion pattern. The weekly Indian Ocean Dipole index reached +0.44°C at 26 July — the first week at or above the +0.4°C threshold for a positive IOD. The Bureau stresses that a single week does not make an event; sustained values are required before a positive IOD is declared.

The prospect matters because of how the two drivers interact. A positive IOD — cooler water near Indonesia, warmer water in the western Indian Ocean — and El Niño have historically reinforced each other's drying influence over Australia. When both are active, as in several notable drought years, the odds of below-average rainfall across much of the country shorten considerably. The WMO's July global outlook likewise forecasts a positive IOD developing alongside the Pacific event.

Drier odds, with a caveat

The Bureau expects El Niño conditions to persist well into the latter half of 2026. The typical influence for Australia is a drier winter–spring for the central and eastern parts of the continent — the pattern that has historically accompanied reduced streamflows, elevated fire danger heading into summer, and pressure on cropping regions through the growing season. The broader worldwide footprint of the event is mapped in our guide to global impacts.

But BOM pairs the outlook with a characteristic note of restraint: "A strong El Niño signal in the tropical Pacific does not necessarily mean strong impacts on Australia's climate." The historical record backs the caution — some of Australia's strongest Pacific events have produced middling local impacts, and some modest events severe ones. The index measures the ocean, not the outcome.

The season ahead

With the central Pacific still warming and international forecasts pointing to a peak late in the year — a trajectory traced in our event timeline — the next few months of the Bureau's fortnightly updates will be watched closely on two fronts: whether the IOD index holds above threshold long enough to confirm a positive event, and whether the spring rainfall outlooks tighten further toward the dry end. For Australian agriculture and water managers, that combination, more than any single index value, will define what the 2026 El Niño means on the ground.