Confusing El Nino signals in the Pacific

Variable relief in sight


Weather
Unusually warm weather is playing havoc with old-school forecasting models.

Unusually warm weather is playing havoc with old-school forecasting models.

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The occasional rain event in the south east is likely to continue but will unlikely overcome the deficiencies established in 2018 – especially in Victoria and southern and central inland NSW.

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The occasional rain event in the south east is likely to continue but will unlikely overcome the deficiencies established in 2018 – especially in Victoria and southern and central inland NSW.

As far as the current atmospheric circulation is concerned, in the broad scale pattern, an El Niño is expected to form – although it is likely to be a weak event.

It is expected to continue through the Southern Hemisphere summer, at about an 80 per cent chance, into early autumn (55-60 pc) before a neutral pattern returns.

At the moment a neutral pattern is still persisting, despite widespread above-average sea surface temperatures across the equatorial Pacific Ocean. As noted previously, this is unusual in such a developing situation.

Despite the warmer than average waters in the tropical western Pacific, Coral Sea and parts of the Tasman Sea, atmospheric convection has remained slightly suppressed in the tropical Pacific near Australia.

The Southern Oscillation index (30 day running mean) is close to zero, so the overall ocean-atmosphere system continues to reflect this neutral pattern but most international models favor formation of a weak El Niño in coming weeks. 

The Indian Ocean Dipole (IOD) has been slightly positive for a few months reducing potential for any moisture from that source to drift across the continent. This positive IOD event is expected to break down in coming weeks because of the monsoon trough in the north east Indian Ocean.The IOD typically has little influence on Australian climate December to April. 

So, in summary, rainfall in Victoria and inland NSW will likely struggle to reach average with a considerable dependence on the occasional rain event, which is likely to be patchy and quite variable in its effect.

In coastal NSW, the NE of the state and at least eastern Queensland, rainfall will be closer to normal but only in isolated pockets will it be sufficient to overcome the effects of the lower rainfall in the past year.

Regarding temperatures, the weak El Niño, along with slightly warmer than average SSTs, means there is a 70-80 pc chance that summer temps will exceed normal in most of the eastern states, but only a 50-60 pc chance in eastern and SE NSW, where at least December temps will be closer to normal.

In South Australia, Victoria and southern NSW, the hottest summer weather is likely to be in the second half of summer and into early autumn. Minimum temps are also expected to exceed longterm norms.

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