RAIN events affected small parts of northern NSW and inland Queensland in the past week and these small “on off” events are favoured to persist through the coming months.
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The major problem is that they will affect only limited areas and there will not be many of them. As a result, many areas will continue to miss out and therefore moisture deficiencies will increase in these regions.
Such events are likely to continue while the El Niño–Southern Oscillation (ENSO) remains neutral, as it is at the moment and likely to remain so for at least the rest of winter.
However, the majority of the climate model outlooks as well as recent warming in the tropical eastern Pacific Ocean mean there is a greater than usual chance of El Niño forming later this year.
Sea surface temperatures in the central to eastern tropical Pacific Ocean have been slowly warming for the past three months along with sub surface waters.
These things are often an indicator of El Niño.
In the atmosphere, indicators the Southern Oscillation Index (SOI) is in the neutral range but tending into the negative portion of that range (finishing last month around -6 when the neutral range is between -7 and + 7).
Also, the trade winds are weaker than average in parts of the central Pacific.
Both these features are indicative of a developing El Niño.
In the west, the Indian Ocean Dipole (IOD) remains slightly negative which is one of the few positive signs and partially responsible for the prognosis of the occasional limited rain events mentioned above.
However, the outlook for spring and early summer has few positive signs at the moment and a greater dependence on these random events will be essential if an El Niño develops.
It is worth remembering that the effects of El Niño events are notoriously challenging to forecast.
At the moment only five out of the eight major international models are predicting an El Niño to develop this year – so it is by no means certain.
In addition, although an El Niño is associated with lower rainfall in eastern Australia, in at least 25 per cent of recent events, the effect on overall rainfall has been minimal.
