Bureau of Meteorology forecasting La Nina this spring
A clearer picture of whether Australian farmers can expect a wetter-than-average spring is emerging from latest Bureau of Meteorology climate modelling. This is what we may expect.
A WETTER-than-average La Nina weather phenomenon this spring is becoming more and more likely, the Bureau of Meteorology said today.
In its fortnightly update, the BOM said recent cooling of the surface of the tropical Pacific Ocean, changes in tropical weather patterns and continued ocean cooling forecast by climate models suggested La Nina could become established within the next three months.
“The Bureau’s ENSO Outlook remains at La Nina Alert ... this means the chance of La Nina forming in 2020 is around 70 per cent — roughly three times the average likelihood,” the BOM said.
“While most key indicators remain within ENSO-neutral range, there have been further signs of La Nina development in the past fortnight. The central tropical Pacific Ocean has continued to cool and trade winds remain stronger than average, while the Southern Oscillation Index has exceeded La Nina thresholds in recent days. Equatorial cloudiness near the Date Line also remains below average.”
The BOM said all of the surveyed international climate models anticipated further cooling of the tropical Pacific Ocean. Five of the eight models reach or exceed La Nina thresholds during October, with six models indicating that if La Nina forms it is likely to persist into December.
“Large parts of the Indian Ocean are warmer than average, with some weak cool anomalies in the west of the basin,” the BOM said. “The Indian Ocean Dipole index has now been at negative IOD levels for three consecutive weeks. More than half of the surveyed models indicate a negative IOD is likely for spring. To be considered a negative IOD event, these values would need to be sustained for at least eight weeks.
“Both La Nina and negative IOD typically increase the chance of above average rainfall across much of Australia during spring.”
The BOM also said climate change was influencing the Australian climate, claiming it had warmed about 1.4C since 1910 while “southern Australia has seen a 10-20 per cent reduction in April-October rainfall in recent decades”.
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