Friday 31 March 2023

La Niña likely likely to continue until at least February 2021, says Bom

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MELBOURNE, Australia – La Niña continues in the tropical Pacific. Australian and international climate models suggest it is likely to continue at least into February 2021, says the Bureau of Meteorology of the Australian Government in its latest Climate Driver Upadate. Central and eastern tropical Pacific Ocean sea surface temperatures remain at La Niña levels, as do most atmospheric indicators, including trade winds and cloudiness. 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.

La Niña weather system is prolonging the rainy season in Vietnam’s Central Highlands, the country’s largest coffee-producing region. The wet weather is preventing coffee beans from ripening as Vietnam’s Buon Ma Thuot Coffee Association said last Monday that only 10% of the coffee trees in the Central Highlands have ripe fruit, much lower than previous years.

The ENSO’s negative phase may also boost global coffee prices by cutting Brazil’s harvest in 2021, Bloomberg News reported, reversing cooler and wetter conditions last year. The last comparable event was between 2010 and 2012. In Colombia, La Niña tends to bring adverse above-average rains.

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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