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The La Nina has become established in the tropical Pacific with both atmospheric and oceanic indicators reaching values consistent with a mature event. During a La Nina, the eastern basin of the Pacific cools while the western basin warms up, upsetting world-wide weather patterns.
The La Nina may have been a work-in-progress during the June-September Indian monsoon, but on hindsight, it appears to have played a role in boosting this year’s rainfall (surplus of nine per cent), though there is no direct cause-effect relationship between the two.
Relatively strong event
The Australian Bureau of Meteorology (BoM) has said in its latest update that all surveyed international models predict that the La Nina may persist until at least February 2021. Other climate models indicate that the current event may be a ‘relatively strong’ one.
The La Nina may fire up the coming Australian tropical cyclone season, which officially commences on November 1. More cyclones than in non-La Nina years are to be expected, and the current outlook indicates a 66 per cent chance of more than average cyclone numbers.
Meanwhile, Indian Ocean Dipole (IOD) that mirrors El Nino-La Nina in the Indian Ocean continues to spook forecasters with values rising in the past two weeks. Only two of the surveyed climate models indicate negative IOD thresholds may be reached in November.
Rains aid winter grains, oilseeds
Early forecasts favoured the development of a negative IOD (warming in the eastern basin relative to the west) but most models (other than two mentioned) lean more towards a positive IOD, record-high values of which last year had caused a massive drought and bushfires in Australia.
Scattered showers last week in South Australia, Victoria, and New South Wales helped maintain the good to locally excellent yield potential of reproductive winter grains and oilseeds. But much less rain fell over the Western Australia wheat belt, the US Department of Agriculture said.
Dry spell in wheat belt
The relatively dry weather has been unfavourable for winter crops, potentially reducing the yield prospects of some advancing through critical reproductive stages of development. Elsewhere in the wheat belt, mostly dry weather persisted in major crop-producing areas of southern Queensland.
The dryness hastened the development of immature winter wheat, while the lack of topsoil moisture likely slowed planting of sorghum and other dryland summer crops. However, sowing of cotton and other irrigated summer crops probably began in some areas.
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