Weather In Focus | Autumn’s late arrival

Autumn’s late arrival


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The gradual transition to autumn weather patterns has temporarily stalled again and the chances of a rain event in the south western half of the state in the next two to three weeks remains low.

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THE gradual transition to autumn weather patterns has temporarily stalled again and the chances of a rain event in the south western half of the state in the next two to three weeks remains low.

It is a different story, however, for coastal NSW.

The controlling climatic indicator at the moment is a neutral ENSO pattern in both the Pacific and Indian Oceans and as a result, the most likely scenario for our weather in the coming months will continue to be extended periods of stable weather with the occasional significant rain event effecting only part of the state each time.

Again, the parts more likely to be effected by such events will be the coast and ranges.

An analysis of many forecasting models comes to the conclusion that a neutral pattern is at least a 50/50 chance of persisting until the start of spring.

A gradual increase in the chance of an El Nino pattern developing occurs in spring but it is as late a November, that it becomes slightly more likely than the neutral set up.

However, a complicating factor is the continuation of above normal sea surface temperatures (SSTs) around a lot of the continent and lack of certainty on what is going to happen in the Indian Ocean.

There is some thought that the Indian Ocean Dipole (IOD), which is influenced by sea surface temps in the Indian Ocean could drift a little into the negative next month and this increases the potential for rain events in the south-eastern states in early winter.

So in summary, for those looking for late autumn and winter rains, the potential IOD is a positive sign, as in the warm SSTs around the country.

The neutral ENSO pattern in the Pacific is neither positive nor negative while the local synoptic (short term) patterns remain negative.

Overall, slightly more positives than negatives to weigh up.

Consequently this could mean a return to at least average rainfall in May and winter in many parts of the state, although – as stated previously – this is dependent on local rain events which will be separated by extended periods of warmer than normal, stable weather.

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