The Outlook | Spring El Nino a 45pc chance

Spring El Nino a 45pc chance


A range of international models indicate about a 45pc chance that a weak El Nino event will return in spring.


AS HAS been the case for many weeks now, the local synoptic weather patterns are providing more stable weather to non-tropical Australia and although it is unusual for such a pattern to persist for this length of time in summer, there are no indications that it will break down soon. 

The pattern has been dominated by a large high well out over the Indian Ocean, ridging through the Bight periodically to south-eastern Australia but only weakly. 

However, such ridging over southern Australia prevents periods of onshore winds developing on the east coast which typically bring in moisture at this time of year. 

When it does eventually break down, as it will, a more normal late summer/early autumn weather pattern is likely to allow the climatic indicators to become more influential again. 

Two of these climate indicators, (namely the above average sea surface temperature around eastern and southern Australia and the Southern Oscillation Index which is positive) would indicate potential for at least average rainfall in the coming months for NSW. 

Others, such as the weakening south-eastern trade winds in the tropical western Pacific indicate that the weak La Nina event that has been in place for the past couple of months is weakening. 

However, most models have indicated this weakening and the likelihood of a return to a neutral pattern for at least the next 6 months seems to be the favoured scenario. 

As for the Indian Ocean, the Indian Ocean Dipole (IOD) remains neutral or very slightly negative. 

Its effect on NSW weather is minimal before April but it continuing neutral into early winter, along with a neutral pattern in the Pacific as well, offers a bit of hope that once this local synoptic situation breaks down, then at least normal rainfall patterns will develop and persist for some months. 

However, in terms of probability, the chance that rainfall in autumn will exceed normal is around 55 per cent in northern and east NSW and 45pc in the south-west. 

The longer term remains a little unclear with a range of international models indicating about a 45pc chance that a weak El Nino event will return in spring.


From the front page

Sponsored by