The Outlook | Weather pattern more ‘neutral’ than El Nino

Weather pattern more ‘neutral’ than El Nino


The 30-day running mean of the SOI is actually slightly positive and nowhere near the El Nino threshold of around -7.


OCCASIONAL patchy rain events continue to affect many parts of eastern Australia so reasonable rainfall levels are now likely to see out the year. In some areas, rainfall will be more the result of storms so variability will be high.

The weather patterns are developing in a way that is more typical of neutral conditions than a weak El Nino.

This is despite the fact  sea surface temperature patterns in the tropical Pacific Ocean have already exceeded El Nino thresholds for five to six weeks now.

However, the atmospheric indicators, such as the strength of the trade winds and the Southern Oscillation Index have not reached El Nino levels.

The 30-day running mean of the SOI is actually slightly positive and nowhere near the El Nino threshold of around -7.

This implies the tropical ocean and atmosphere are not reinforcing each other and this is usually required to establish and sustain any El Nino event and its influences on the weather in eastern Australia.

While this situation remains, then the effects of the El Nino will be minimal.

It is unlikely to have a significant effect on moisture availability, as this will be helped by above average sea surface temperatures, especially in the tropical western Pacific.

Consequently, the main effects of this year’s developing El Nino will be warmer than normal summer temperature. 

The Indian Ocean SSTs remain cool and the Indian Ocean Dipole is slightly-positive.

Its effect is fairly non-existent from now until April because the influence of the northern monsoon takes over.

The monsoon is slow to develop this year and in the long term, the cooler waters could also reduce rainfall potential if it persists into autumn.

It also means that moisture availability from this source will be lacking for at least the first half of summer and there will be a need for greater dependence of moisture flow into eastern Australia from the north and north east.

At the moment this source is more than compensating and so the prospects for reasonable rain in the next month are fairly good.

In 2019, indications are for neutral conditions in the Pacific basin for much of the year and if this remains the case, it will mean warmer than normal weather (for the majority of the months) and that overall rainfall in the eastern states will end up close to or slightly up on normal, but significant rain is required to overcome the deficiencies already established and unfortunately, such events might be few and far between.


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