Australia just recorded its 9th-wettest October since national rainfall observations started in 1900, with above-average rainfall in all states and territories except Tasmania.

So why did this happen during the current strong phase of El Niño, a climate driver which typically brings drier weather to most of Australia at this time of year?

Here are the main reasons why October 2026 was generally wet in Australia despite El Niño:

Warmer than average sea-surface temperatures around Australia

El Niño tends to reduce rainfall over Australia during winter and spring (and especially in large parts of southern and eastern Australia) by weakening the trade winds that blow moisture-laden air towards the country from the tropical Pacific Ocean.

But as Weatherzone meteorologist Ben Domensino explains, "Warmer-than-average water near Australia can supply the atmosphere with additional moisture via enhanced evaporation, which can counteract the drying influence of El Niño."

Image: Sea surface temperature anomalies around Australia on November 1, 2026. Source: BoM.

As the chart above illustrates, sea surface temperatures were around a degree above average at the start of November in waters surrounding significant portions of Australia. The pattern was similar during October.

Warm Indian Ocean waters negate typical effects of both El Niño and positive IOD

Image: Sea surface temperature anomalies on October 26, 2026, showing a large area of warmer than normal water just south of the tropics and outside the labelled IOD monitoring regions. Source: NOAA.

While El Niño is a Pacific Ocean phenomenon, the dynamics of the Indian Ocean also influence Australia's weather.

The Indian Ocean Dipole (IOD) is an index that monitors changes in sea surface temperatures on either side of the tropical Indian Ocean. Like El Niño, the different phases of the IOD typically affect Australia's weather in different ways.

On October 27, the BoM declared that a positive IOD event was underway, after the IOD Index exceeded the positive threshold for seven consecutive weeks.

A positive IOD means that surface waters in the eastern tropical Indian Ocean (near Indonesia) are consistently cooler than the western tropical Indian Ocean, and it typically results in less moisture-laden air (and associated rainfall) flowing towards Australia from the northwest.

Image: Typical features and impacts of a positive IOD. Source: Weatherzone.

The combination of a positive IOD and a strong El Niño would ordinarily provide two strong pointers to a predominantly dry weather pattern across much of Australia during October.

But their effects throughout October were largely negated (and could continue to be defied in November) by a large area of warmer-than-average water in the south–central Indian Ocean, sitting just south of the IOD monitoring regions in the tropics.

During October, moisture streamed across the country on several occasions from the part of the Indian Ocean where the warm "blob" was located. 

Warmer-than-average waters east of Australia also played a significant role.

The largely stagnant Tasman Sea high pressure system in mid-October

In mid-October, a large, very slow-moving high pressure system drifted out over the Tasman Sea and effectively "parked" itself there for around a week. Air circulating anti-clockwise around this high pushed moisture-laden air from both the Tasman and Coral Seas towards Queensland and northeastern New South Wales.

The prolonged mid-month wet spell helped Queensland as a whole register its second-wettest October on record, while rainfall was the highest on record for parts of the Central Highlands and Coalfields, Central West, Maranoa and Warrego, and Wide Bay and Burnett forecast districts.

Image: Australian rainfall deciles in October, 2026. Source: BoM.

Short-term outlook: can we expect more widespread rain in November despite El Niño and the positive IOD?

"The positive IOD is still expected to restrict the amount of available moisture to generate rainfall across the Australian region in coming months, although it’s strongest impacts may be to the north of the country," Ben Domensino explains.

"This dry influence will also be enhanced by El Niño in the tropical Pacific Ocean."

As the map below shows, Tasmania faces another potentially drier-than-average month, while southern Victoria could also miss out on significant rainfall. If so, Melbourne parks and gardens should stay green for now after 113.8 mm accumulated in the city gauge during October, the wettest month of 2026 to date.

Image: Chance of exceeding the median rainfall during November 2026, according to the Bureau of Meteorology’s ACCESS-S model. Source: BoM.

At this stage, forecast models are also expecting wetter-than-average conditions for most of Australia in December.