Spring easterlies may bring isolated rainfall | The Outlook

Spring easterlies may bring isolated rainfall | The Outlook


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The Pacific basin is in a neutral phase and all international models indicate that this is likely to be the case for the rest of the year and into 2020.

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ONCE again, most medium term climate indicators have shown minimal change in the past couple of weeks and there is no reason to change the current favoured scenario of further drier than average months but with the potential for the one-off event increasing through spring.

The Pacific basin is in a neutral phase and all international models indicate that this is likely to be the case for the rest of the year and into 2020.

Although the sea surface temperature (SST) patterns have been neutral for some time in the Pacific, the atmosphere is now also taking on a neutral appearance as well, with the Southern Oscillation Index back around zero, in the middle of the neutral range after being in the El Nino range of lower than -7 in May and June.

The SSTs also remain up on normal in the Tasman Sea and across the central and western tropical Pacific.

The combination of this and a neutral pattern will encourage the one-off rain event when the synoptic patterns start to favour a more easterly based flow into eastern Australia which usually starts around the middle of spring.

To the west, the Indian Ocean remains a bit of a problem.

The Indian Ocean Dipole remains positive with warmer than average sea surface temperatures in the central and western tropical Indian Ocean, and slightly cooler than average waters in the tropical Indian Ocean between north-west Australia and Indonesia, although there are signs waters could be warming up a little in this region which would be a positive sign.

However, the influence of the IOD on south-eastern Australian rainfall decreases significantly after mid spring.

The Southern Annular Mode (SAM) remains negative, but the potential for change is always high with SAM.

Remember, when it is negative, the Southern Ocean westerlies move further north and increase the chance of rainfall in Victoria, southern NSW and south-eastern South Australia which is also good news for the snowfields of south-eastern Australia but bad news for coastal and northern NSW and Queensland where westerlies bring little if any rain.

So the prognosis for continuation slightly below average rainfall for the coming months remains unchanged.

The occasional one-off event could be a useful boost to rainfall in limited areas especially from mid spring and this provides the best opportunity for mid to late spring rain in patches.

Further into spring and early summer, rainfall is likely to be near normal - better than in recent years, but still unlikely to be sufficient to overcome the major deficiencies established by the drier years of recent times.

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