La Nina will last until early fall, according to the Bureau of Meteorology | border mail


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The current La Nina weather phase, correlated with above-average rainfall in many parts of Australia, is expected to continue at least until early autumn according to the Bureau of Meteorology. In its latest Climate Drivers Report, released this week, the BoM said most of the models it had studied indicated that the La Nina event in the Pacific Ocean was expected to persist into the fall, potentially providing a catalyst for an early break for the winter cropping season in some regions. Sea surface temperatures in the central and eastern tropical Pacific are typical of a mature La Nina event. Colder water is present below the surface, supporting cooler waters at the surface. In the atmosphere, patterns are also broadly typical of La Nina, with decreasing cloudiness near the International Date Line, moderate to strong positive Southern Oscillation Index (SOI) values, and generally increased trade winds. Atmospheric and oceanic models reinforce each other in a positive feedback loop, which the BoM calls “coupling”. This coupling of key factors allows the La Nina pattern to hold for an extended period. In terms of other climatic phenomena that may impact Australia’s weather in late summer, the BoM said the Madden-Julian Oscillation (MJO) is currently in the eastern Pacific and is expected to remain in this region next week before weakening, which correlates with drier than average weather over northwestern Australia, including the Northern Territory Top End. IN OTHER NEWS: This could also temporarily weaken some La Nina indicators as trade winds typically weaken across the Western Pacific in this phase of the MJO. The Southern Annular Mode (SAM) index is currently neutral. It should approach positive levels for the remainder of January. A positive SAM during the summer generally brings wetter weather to eastern Australia, but drier than average conditions for western Tasmania. The Indian Ocean Dipole (IOD) remains neutral, but generally has little influence on global weather from December to April anyway.



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