Tropical Pacific Ocean likely to cool, but remain ENSO-neutral
The El Niño–Southern Oscillation (ENSO) is currently neutral. Sea surface temperatures (SSTs) in the central tropical Pacific Ocean are near average, despite slowly cooling over the past two months. Waters beneath the surface are slightly cooler than average.
While most models indicate SSTs in the central tropical Pacific are likely to continue cooling over the coming months, ENSO-neutral is favoured to persist. Only two of the seven models surveyed suggest SSTs will remain cool for long enough to be considered a La Niña event. This cooling of the tropical Pacific may be contributing to the wetter than median climate outlooks in Australia.
Most climate models predict the negative Indian Ocean Dipole (IOD) event will persist through the southern hemisphere spring, despite current values rising marginally above the −0.4 °C threshold. Stronger-than-usual easterly winds across the tropical eastern Indian Ocean over the last three weeks have weakened the IOD event, however, this is most likely to be temporary. A majority of the five climate models surveyed by the Bureau predict the negative IOD will persist into November. A negative IOD increases the chance of above average winter–spring rainfall for much of southern and eastern Australia.
The Madden–Julian Oscillation (MJO) is currently in the western Indian Ocean, where it has remained since early August. This phase of the MJO typically sees increased cloudiness over the Southeast Asian parts of the Maritime Continent and eastern Indian Ocean, along with enhanced easterly wind anomalies, which may have acted to weaken the negative IOD. Forecasts generally indicate a weak MJO will progress eastwards across the Indian Ocean in the coming week.
The Southern Annular Mode (SAM) index has been positive over the past week and is forecast to remain so for the next fortnight. A positive SAM typically has a drying influence on south-west and south-east Australia during winter, and enhances chances of above average rainfall over much of New South Wales during spring.
Climate change continues to influence Australian and global climate. Australia's climate has warmed by 1.44 ± 0.24 °C over 1910–2019, while southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades.
Next Climate Driver Update expected on 14 September 2021.Climate Driver
Daily maximum temperature extremes graph for Australia: 1 January to 31 August 2021
Above median spring rainfall likely for eastern two-thirds of Australia
Issued: 26 August 2021
- Rainfall for spring (September to November) is likely to be above median for south-east WA, the NT, SA, Queensland, NSW, Victoria and eastern Tasmania (chance of exceeding median is greater than 60%). Much of the eastern States show a greater than 80% chance, as does eastern parts of the NT and SA. Conversely, parts of western WA and south-west Tasmania are likely to have below median rainfall (chance of exceeding the median is less than 40%).
- The pattern for the months of September and October is similar to the spring outlook, though the likelihood of exceeding the median rainfall is not as high in the eastern two-thirds of the country, and extends further west into eastern WA for September.
- Rainfall for October to December is likely to be above median for the eastern half of Australia, and below median for north-west WA.
- Past accuracy (Opens in new window) for September to November rainfall is high to very high for most of the eastern two-thirds of Australia, with moderate accuracy for central and eastern Victoria, most of WA and the central NT shifting to low accuracy for central areas of WA.
