MELBOURNE, Australia – The El Niño event continues in the tropical Pacific reports the Bureau of Meteorology of the Australian Government in its latest update. The typical drying influence of El Niño on Australia’s climate usually reduces during summer, especially in the east; however, below median rainfall is still often observed in north-east Australia.
As we have seen this year and in the historical data, high-impact rainfall events can occur during El Niño years, particularly during October to April when severe storm frequency peaks.
Model forecasts indicate the warmth of sea surface temperatures (SSTs) is likely at or near its peak, with SSTs expected to remain above El Niño thresholds into the southern hemisphere autumn 2024. Some atmospheric indicators have weakened over the past three weeks, and the SOI is currently neutral.
The Southern Annular Mode (SAM) is currently positive. The SAM index is expected to decrease slightly, but stay near the positive SAM threshold for the coming fortnight.
During austral summer, a positive SAM historically increases the chance of above average rainfall for parts of eastern NSW, south-eastern Queensland, eastern Victoria, and north-east Tasmania, but increases the chance of below average rainfall for western Tasmania. Rainfall increases are due to the positive SAM shifting westerly winds further south, increasing onshore flow over south-east Australia.
The positive Indian Ocean Dipole (IOD) event is weakening steadily. IOD events typically break down as the monsoon trough shifts south into the southern hemisphere, typically at the end of spring, meaning the breakdown this year has been later than usual. Model forecasts suggest the positive IOD is likely to continue to ease over the coming weeks, with the majority indicating the IOD index will fall below +0.4 °C in January.
The Madden–Julian Oscillation (MJO) is currently over the Indian Ocean. In the coming weeks, international climate models suggest it is likely to move across the Maritime Continent, strengthening as it shifts into Australian longitudes. At this time of year, when the MJO is in the western Maritime Continent, the chance of above average rainfall typically increases across central Australia. When the MJO is in the eastern parts of the Maritime Continent, the chance of above average rainfall typically increases across northern Australia, and provides a favourable environment for the onset of the monsoon in Darwin.
Global warming – global sea surface temperatures (SSTs) were highest on record for their respective months during April to November. Forecast unusually warm sea surface temperatures (SSTs) in the Tasman Sea may also be contributing to a chance of above median summer rainfall over parts of Australia.
Australia’s climate has warmed by 1.48 ± 0.23 °C since national records began in 1910. There has been an increase in extreme heat and fire weather associated with the warming. There has also been a trend towards a greater proportion of rainfall from high intensity, short duration rainfall events, especially across northern Australia.
