La Niña likely to continue until at least the end of summer 2020−21

Image: Bureau of Meteorology

Vineyards could be in for a rough go this vintage as the Bureau of Meteorology (BOM) says the La Niña weather phenomenon is continuing on and will likely do so until early next year.

According to the BOM, La Niña continues in the tropical Pacific. Australian and international climate models suggest it is likely to continue at least into February 2021.

Central and eastern tropical Pacific Ocean sea surface temperatures remain at La Niña levels, as do most atmospheric indicators, including trade winds and cloudiness, according to the BOM.

The Southern Oscillation Index (SOI) has moved back into neutral values, most likely due to the influence of a passing MJO event. The SOI is expected to return to La Niña levels in the coming weeks.

La Niña typically increases the chance of above average rainfall across much of Australia during spring, and across eastern Australia during summer. Current climate outlooks indicate rainfall during November 2020 to January 2021 is likely to be above average for most of the country.

Most models suggest La Niña will peak in December, with around half the models anticipating a strong event. While there is some possibility that the peak strength could reach levels similar to 2010–12 there are some differences.

La Niña became established much earlier in 2010, was long-lived (over two years), and impacts were enhanced by a negative Indian Ocean Dipole and warm ocean temperatures around Australia.

In contrast, the Indian Ocean Dipole (IOD) is currently neutral, and most models suggest it will remain neutral for the rest of 2020.

The Southern Annular Mode (SAM) is expected to be positive for the remainder of October into early November. La Niña tends to favour positive SAM during spring and summer, further supporting the likelihood of above average rainfall in the east.

The Madden–Julian Oscillation (MJO) is currently in the western Pacific and is expected to remain moderately strong as it moves across the Pacific basin, then decrease in strength as it approaches Africa.

Climate change is also influencing the Australian climate. Australia’s climate has warmed by around 1.4 °C since 1910, while southern Australia has seen a 10–20% reduction in cool season (April–October) rainfall in recent decades.

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