La Nina influences set to last into autumn

La Nina influences set to last into autumn | The Outlook


The official onset of the monsoon in Darwin occurred in the week before Christmas and about a month earlier than last year.


A WELL established La Nina event will dominate weather patterns in eastern Australia for at least another two months.

The La Nina is likely to weaken in February and the patterns are favoured to return to a neutral set-up by later in March or April.

The official onset of the monsoon in Darwin occurred in the week before Christmas and about a month earlier than last year.

This is a source of moisture for south-east Queensland and NSW and access to this moisture will continue periodically in the coming weeks.

The Pacific Ocean continues to sit in a La Nina state.

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A large pool of cool water persists across the eastern half of the tropical Pacific Ocean with warm water persisting in the western half - a typical La Nina set-up.

However, cool water anomalies below the surface in the eastern Pacific are beginning to warm in the past week or two and this implies that we are near or at the peak of this La Nina.

With less cool water to upwell to the surface we would expect the La Nina to begin to weaken later in January and into February before possibly tending to a neutral state by later in March.

However, because there can sometimes be a lag between ocean and the atmosphere, it is expected the La Nina influences will persist for some time.

In the tropics, the Madden Julien Oscillation modelling suggests another active phase in the Australian region by mid-January and this could persist for the remainder of the month, which would be conducive to significant rainfall events and also lead to an increased chance of tropical cyclone activity at those times.

Rain events are more likely in the north and east of NSW and over Queensland but occasional phases will extend into south west NSW and Victoria, but with lower rainfall likely.

Southern Ocean westerlies have been pushed well to the south by the La Nina pattern, and consequently the Southern Annular Mode will have little influence on the weather in eastern Australia for a couple of months.

In addition, the Indian Ocean Dipole continues to remain near zero (neutral) and as a result, the Indian Ocean is unlikely to have much of an impact of our weather now before mid-autumn.

Finally, the sea surface temperature patterns around continental Australia remain above normal except for far south west of Australia.

Consequently, onshore winds will pick up a little more moisture - another factor adding to the potential for increased rainfall to persist.

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