Thursday 25 July 2024
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La Niña and negative Indian Ocean Dipole continue, reports BOM

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MELBOURNE, Australia – La Niña continues. According to the Bureau of Meteorology (BOM) of the Australian Government, in the tropical Pacific Ocean 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 a return to ENSO-neutral conditions (neither La Niña nor El Niño) early in 2023.

La Niña typically increases the chance of above average rainfall for northern and eastern Australia during spring and summer.

The negative Indian Ocean Dipole (IOD) event also 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 into late spring before rapidly decaying. A negative IOD typically increases the chance of above average spring rainfall for most of the eastern two thirds of Australia.

The Southern Annular Mode (SAM) is currently in a neutral phase. However, SAM is likely to return to a positive phase during November and remain generally positive into early summer. During the spring and summer months, a positive SAM increases the chance of above average rainfall for parts of eastern New South Wales, eastern Victoria, and south-eastern Queensland, and increases the chance of below average rainfall for western Tasmania.

The Madden-Julian Oscillation (MJO) is currently active over the western Pacific Ocean. Most models indicate the pulse is likely to track slowly eastwards across the western Pacific region at moderate strength over the coming fortnight. The MJO’s influence at this time of the year may lead to above-average rainfall for parts of eastern Australia, and briefly reduce the strength of equatorial trade winds west of the Date Line.

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 Bureau of Meteorology’s extended and long-range forecasts show that above average rainfall is likely across much of eastern 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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