IT IS becoming increasingly likely that the La Nina pattern in the Pacific Ocean will persist at least until early autumn and as a result generally above average rainfall is expected over the next three months with an enhanced potential for heavy rainfall events occurring.
However rainfall may be characterised by periods of heavy rain mixed in with periods of little rainfall - that is, fewer rain days, but heavier rain days when they occur.
This was not the case in November when the Southern Annular Mode fluctuated but was often negative and even in early December, the Southern Ocean westerly winds were further north than normal and not a pattern expected with a La Nina, but that doesn't mean the La Nina is weakening or going away.
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A large mass of cooler than normal water continues to lie across the eastern Pacific Ocean while the western Pacific Ocean remains above average. This is, by definition, a La Nina.
Historically, not all La Nina events are wet, and it's certainly possible (although rare) to have marked periods of hotter and drier weather mixed in with periods of wetter conditions.
Ultimately, the La Nina sets up a pattern where easterly winds are more favoured to occur and persist across the western Pacific Ocean.
This pushes higher levels of moisture into eastern Australia, which provides one of the essential ingredients into the production of rainfall across the eastern half of the country.
However, the synoptic patterns that dominated the second half of November and first few days of December are changing.
They are expected to become more typical of La Nina patterns in the Pacific Ocean (that is, higher chance of easterly ridging and easterly winds pushing into eastern Australia) from around the middle of December when a Madden-Julian pulse in the tropics could also be around to enhance moisture availability.
It is likely that overall synoptic patterns will be more La Nina-like during January and February also.
That means generally stronger ridging along the east coast which should help bring maximum temperatures closer to average for this period and feed in more moisture from the east.
To the west, the Indian Ocean likely to remain neutral during this time.
There has been little moisture feeding in from the north-west for some months now.
The Indian Ocean Dipole is neutral but unlikely to influence the weather much in the coming months.
The reduction in the so-called north-west cloud bands will also limit the potential for the widespread bands of rain in summer which supported the La Nina in 2010-11 bringing record rainfalls at that time.
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