The Bureau’s El Niño Alert continues, with El Niño development considered likely during spring.
When El Niño Alert criteria have been met in the past, the Bureau says, an El Niño event has developed around 70pc of the time.
Sea surface temperatures (SSTs) in the tropical Pacific are exceeding El Niño thresholds and have continued to warm slightly over the last fortnight. SSTs are likely to remain above El Niño thresholds until at least early 2024.
The 90-day Southern Oscillation Index (SOI) is presently just below El Niño thresholds, However, atmospheric indicators suggest that the Pacific Ocean and atmosphere are not yet consistently reinforcing each other, as occurs during El Niño events.
The latest weekly Indian Ocean Dipole (IOD) index is +1.05 °C, being the second week above the positive IOD threshold of +0.40 °C. However, before an IOD event is declared, several more weeks of the IOD index above the positive IOD threshold are required. A positive IOD typically decreases spring rainfall for central and south-east Australia and can increase the drying influence of El Niño.
The Madden–Julian Oscillation (MJO) is currently weak or indiscernible, and is likely to move over the Maritime Continent or Western Pacific in the coming days. If this pulse moves into the Western Pacific and remains relatively strong it may assist El Niño development by weakening trade winds.
The Southern Annular Mode (SAM) index is currently at neutral values and is expected to become slightly negative then return to neutral during September. A negative SAM is associated with increased rainfall over south-west Western Australia and western Tasmania during spring, while a neutral SAM is associated with typical climate conditions for Australia.
Australia’s climate has warmed by an average of 1.47 ± 0.24 °C since national records began in 1910. There has also been a trend towards a greater proportion of rainfall from high intensity, short duration rainfall events, especially across northern Australia. Southern Australia has seen a reduction, by 10 to 20%, in cool season.
Source: Bureau of Meteorology