Friday 02 December 2022

La Niña is underway in the tropical Pacific and Enso Outlook remains at La Niña

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MELBOURNE, Australia – La Niña increases the chance of above average rainfall for northern and eastern Australia during the Austral spring and summer, reports the Bureau of Meteorology of the Australian Government. Both atmospheric and oceanic indicators of the El Niño–Southern Oscillation (ENSO) are consistent with an established La Niña, including tropical Pacific sea surface temperatures, the Southern Oscillation Index (SOI), trade wind strength, and equatorial cloudiness.

Models indicate the La Niña may peak during spring and return to neutral conditions early in 2023. Sea surface temperatures in the tropical Pacific have weakened a little compared to two weeks ago while the SOI has continued to rise and is currently well above La Niña thresholds.

The negative Indian Ocean Dipole (IOD) event continues. The IOD index has satisfied negative IOD thresholds (i.e. at or below −0.4 °C) since June. Models indicate that the negative IOD is likely to persist at least until late spring. A negative IOD typically increases the chance of above average spring rainfall for most of the eastern two thirds of Australia.

When La Niña and negative IOD conditions combine, the likelihood of above average rainfall over Australia is further increased, particularly for the eastern half of the continent.

The Southern Annular Mode (SAM) is currently positive and is likely to remain generally positive throughout spring into early summer. During the spring months, positive SAM increases the chance of above average rainfall for parts of eastern New South Wales, eastern Victoria, and south-eastern Queensland, but has a drying influence for western Tasmania.

Most models indicate the Madden–Julian Oscillation (MJO) will strengthen over the Maritime Continent in the coming week and maintain moderate strength as it moves east towards the western Pacific. While active in the Pacific at this time of the year, the MJO increases the chance of above average rainfall over the eastern half of Australia.

Climate change continues to influence Australian and global climate. Australia’s climate has warmed by around 1.47 °C for the 1910–2020 period. There has also been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.

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