Thursday 13 June 2024
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A mature La Niña event to remain active in the tropical Pacific until early autumn

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MELBOURNE, Australia – A mature La Niña event remains active in the tropical Pacific, says the Bureau of Meteorology of the Australian Government in its latest Climate Driver Update. Climate models suggest the 2021–22 La Niña is near or at its peak, with a return to neutral El Niño–Southern Oscillation (ENSO) likely early in the southern hemisphere autumn. Autumn is the usual time of the year in which ENSO events decay and return to neutral.

La Niña increases the chance of above average rainfall across much of northern and eastern Australia during summer. Significant weather can still occur as La Niña weakens, especially as the peak of the Australian tropical cyclone season is around February/March.

Oceanic indicators of ENSO continue to show a clear La Niña signal, with cooler than average sea surface temperatures in the eastern tropical Pacific, and cooler sub-surface waters supporting the cooler waters at the surface. However, these cooler sub-surface waters continue to ease. Most atmospheric indicators also show clear La Niña patterns, with decreased cloudiness along the Date Line and trade winds either close to average or slightly increased. While the 30-day Southern Oscillation Index (SOI) has experienced some short-term fluctuation, the 90-day SOI is still firmly in La Niña territory.

The Madden–Julian Oscillation (MJO) is currently weak, but models indicate it may strengthen in the eastern Indian Ocean or western Maritime Continent in the coming week. Typically, when the MJO is in the eastern Indian Ocean it may provide a boost to La Niña by encouraging strengthened trade winds in the Pacific Ocean. As the MJO approaches the Maritime Continent, an increase in cloudiness and rainfall over northern Australia is more likely.

The Southern Annular Mode (SAM) index has recently risen to positive levels. It is forecast to remain positive, but gradually weaken, over the next three weeks. A positive SAM during summer typically brings wetter weather to eastern parts of Australia, but drier than average conditions for western Tasmania.

The Indian Ocean Dipole (IOD) remains neutral. The IOD typically has little influence on global climate from December to April.

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Climate change continues to influence Australian and global climate. Australia’s climate has warmed by around 1.44 °C for the 1910–2019 period. Rainfall across northern Australia during its wet season (October–April) has increased since the late 1990s. In recent decades there has been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.

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