La Nina called by American forecasters

La Nina called by American forecasters

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A La Nina event is likely to form before the end of the year.

A La Nina event is likely to form before the end of the year.

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American meteorologists have officially called a La Nina event in the Pacific Ocean but the BOM is holding off on a similar call - for now.

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OFFICIAL American forecasters have declared a La Nina event in the Pacific Ocean.

The US-based National Oceanic and Atmospheric Administration (NOAA) has said a La Nina will take place this year after key criteria exceed thresholds.

A La Nina event is correlated with wetter than average conditions in Australia and drier than average conditions in the Americas.

However, the Bureau of Meteorology (BOM) has held off from calling the event just as yet, although in its latest climate driver update, the agency said it believed the phenomenon would be officially in place by October.

Internationally, there is no agreed threshold that determines a La Nina is active and NOAA use a definition of La Nina slightly different to BOM.

The BOM said drivers were falling into place to create a La Nina event.

Waters in the tropical Pacific continue to cool while the BOM noted the atmosphere is responding to the water temperature patterns and coupling to create a true La Nina event.

It said once the La Nina formed it was likely to persist until at least the end of the year, with many models tipping it will endure for the first quarter of 2021.

The La Nina will be a mixed blessing for Australian agriculture.

It will potentially provide invaluable finishing rain for the winter crop and moisture to allow summer croppers to plant.

However, on the flip side, if rain continues through November and December it could potentially cause quality issues with the winter crop.

On the other side of the continent, conditions in the Indian Ocean remain neutral, although the BOM said some models were forecasting an Indian Ocean Dipole (IOD) negative event, again correlated with wetter conditions in Australia.

Another piece of the puzzle is also falling into place for those looking for rain.

The Southern Annular Mode (SAM) is positive for the rest of September.

Positive SAM during spring is typically associated with wetter and cooler than average conditions in parts of eastern Australia.

The story La Nina called by American forecasters first appeared on Farm Online.

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