26 August 2021Next issue 30 June 2022Early rainfall onset likely...

26 August 2021

Next issue 30 June 2022

Early rainfall onset likely for most of northern Australia

An early rainfall onset for the 2021–22 season is likely across most of northern Australia. Most of Queensland and the NT have a greater than 70% chance of an early rainfall onset, with areas in central and south-western Queensland having a greater than 80% likelihood. Areas of WA bordering the NT, and large parts of south-east Queensland have more than a 60% likelihood. Remaining areas of WA have roughly equal chances of an early or late rainfall onset.

The northern rainfall onset outlook gives an indication of whether the first significant rains after 1 September are likely to be earlier or later than median. View median onset dates here.

This is the last issue of the Northern Rainfall Onset outlook for the 2021–22 season. From September 1, please check the observations tab for daily updates of rainfall accumulation and onset status.

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Influences

The northern Australian rainfall onset is affected significantly by the phase of the El Niño–Southern Oscillation (ENSO). ENSO is currently neutral. Most climate model outlooks indicate the central tropical Pacific is likely to cool over the coming months but remain ENSO-neutral. Only one of seven models surveyed by the Bureau indicate this cooling will be sustained enough and cool enough to meet La Niña thresholds in spring or early summer, with two remaining models indicating a brief cooling just to La Niña thresholds. The cooling of the tropical Pacific is likely contributing to the earlier onset likelihood.

In the Indian Ocean, a negative Indian Ocean Dipole is forecast for spring and likely to return to neutral IOD in December, which is typical of the IOD seasonal cycle. This may also be contributing to the higher likelihood of an earlier rainfall onset.