La Niña anticipated to ease over summer

Beef Central, 19/01/2023

La Niña continues in the tropical Pacific, but has weakened from its peak in spring 2022.

Though ocean temperatures have warmed in recent weeks, atmospheric indicators are largely unchanged and remain at La Niña levels.

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

Long-range forecasts suggest that tropical Pacific Ocean temperatures will continue to warm and be at ENSO-neutral levels (neither La Niña nor El Niño) during February, with a change in atmospheric patterns towards neutral levels likely to follow. As accuracy is generally lower for long-range forecasts made at this time of year, ENSO outlooks that extend past autumn should be viewed with caution.

The Indian Ocean Dipole (IOD) is neutral and has little influence on Australian climate while the monsoon trough is in the southern hemisphere (typically December to April).

The Southern Annular Mode (SAM) is strongly positive and is likely to be positive into late-January. During summer, when SAM is positive there is typically an increased chance of above average rainfall for eastern New South Wales, eastern Victoria and north-east Tasmania and below average rainfall for western Tasmania.

The Madden–Julian Oscillation (MJO) has been weak since early January, but most models expect a strengthening pulse to develop over tropical Africa or the western Indian Ocean in the coming days, tracking further east towards the eastern Indian Ocean in the coming fortnight. This may lead to a period of suppressed rainfall across northern Australia, commencing in about a week, after the current weather-generating systems over Australia’s north-east dissipate.

Sea surface temperatures remain warmer than average in the western tropical Pacific, northern Maritime Continent, and to the south and south-east of Australia from the Eyre Peninsula to waters east of New Zealand. Warmer Australian waters, especially in the tropics, can result in greater evaporation, humidity, cloudiness, and rainfall.

Climate change continues to influence Australian and global climates. Australia’s climate has warmed by around 1.47 °C in the period 1910–2021. There has also been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.

Source: Bureau of Meteorology


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