Climate Model Summary

Models indicate increased chance of negative IOD, as La Niña looks to ease over winter

The 2021–22 La Niña continues to weaken with latest observations and outlooks indicating a return to neutral-ENSO by July. All but one of the surveyed models predict neutral, but cooler than average, temperatures in the central tropical Pacific throughout the southern winter. During spring however, the model outlooks show a broader spread in outcomes, with three models indicating a return to La Niña values and four models maintaining neutral-ENSO values. Despite La Niña easing, it's likely that ocean temperature patterns in the Pacific will still contribute to a wetter than average winter across eastern Australia. Model accuracy at this time of year is moderate to high.

The Indian Ocean Dipole (IOD) is neutral but index values have been close to the negative IOD threshold for the last five weeks. All model outlooks indicate a negative IOD event is likely to develop in the coming weeks. A negative IOD event can enhance winter and spring rainfall across much of Australia, as well as influencing rainfall patterns in countries around the Indian Ocean basin. Outlook accuracy is typically low during autumn but increases during the winter months. The consistent outlook for a negative IOD across all the surveyed models provides additional confidence in the outlook. 

NINO3.4 outlook

The latest weekly NINO3.4 value to 12 June 2022 is −0.4 °C, falling well short of the La Niña threshold (−0.8 °C) and suggesting an easing of La Nina. All but one of the seven surveyed models predict neutral, but cooler than average, temperatures in the central tropical Pacific throughout the southern winter.

During spring however, the model outlooks show a broader spread in outcomes, with one model indicating a return to La Niña values from late winter and two additional models touching on La Niña thresholds from mid-spring. The remaining four models maintain neutral-ENSO values. Despite La Niña easing, it is likely that ocean temperature patterns in the Pacific will still contribute to a wetter than average winter across eastern Australia. Model accuracy at this time of year is moderate to high.

La Niña typically increases the chances of above average rainfall for much of eastern Australia during winter and spring. It is not uncommon to experience some La Niña-like conditions when values are close to La Niña thresholds.

Persistent NINO3.4 values above +0.8 °C typically indicate El Niño, while values below −0.8 °C typically indicate La Niña.

Indian Ocean Dipole (IOD) outlook

The IOD remains neutral, but the weekly IOD index briefly dipped below negative IOD thresholds in recent weeks. It is currently just shy of the threshold, recording −0.37 °C for the week ending 12 June 2022. All models surveyed indicate a negative IOD event could develop in the coming weeks, with several forecasting strong negative index values developing by August. A negative IOD increases the chance of above average winter-spring rainfall across much of Australia.

Outlook accuracy is typically low during autumn but increases during the winter months. The consistent outlook for a negative IOD across all the surveyed models provides additional confidence in the outlook. 

Australian Community Climate Earth-System Simulator–Seasonal (ACCESS–S)

The Bureau of Meteorology's climate model generates a six-month forecast for the NINO and IOD indices each fortnight.

The most recent model run (generated 4 June 2022) indicates sea surface temperature in the central tropical Pacific (NINO3.4) are likely to warm to within the neutral ENSO range in June and remain neutral through to at least the start of the southern spring. Model skill is generally moderate to high at this time of year.

The current outlook for the Indian Ocean Dipole (IOD) indicates IOD index values are likely to continue to drop during winter, with strong negative values developing by July. Model accuracy for IOD outlooks at this time of year is relatively low but steadily improves during winter. A negative IOD event typically enhances winter and spring rainfall across much of Australia.

The forecast values, shown below in bold, are for the model's ensemble mean.