Minor changes in the sea surface temperature patterns across the tropical Pacific indicate that the La Nina event is now very weak and borderline neutral conditions are developing.
This is because the tropical Pacific SSTs temperatures have continued to warm and approach neutral values.
Also, the subsurface temperatures are now closer to average than they have been for some time. Trade winds are also close to average strength.
However, some atmospheric indicators continue to be indicative of a La Nina, namely the cloudiness along the equator and especially the Southern Oscillation Index.
The 30-day running mean of the SOI is still around +15, which remains well within the La Nina range.
Although most climate models indicate that a neutral set-up is likely in the Pacific for a few months, a slight majority also favour a return of La Nina conditions in spring leading to a third consecutive summer with such conditions.
It must be emphasised that this assessment remains speculative at this stage but it is a definite possibility.
Even with a return to neutral conditions for the rest of winter, the prognosis for above average rainfall in eastern Australia persists.
This is reinforced by what is happening in the Indian Ocean.
The Indian Ocean Dipole is near -0.5°C, which is below the negative IOD threshold value of 0.4°C. All climate models indicate a negative IOD is likely to persist into spring.
A negative IOD increases the chances of above average winter-spring rainfall for many parts of Australia, especially in the south east states and Queensland.
Its associated increase in cloudiness means that although daytime temperatures will be near or slightly below normal, overnight minimum temperatures will be a little up on normal and frost level minimum temperatures will be less frequent than normal in frost prone areas.
However, the set-up will encourage the occasional brief but significant cold outbreaks in the south east.
Also supporting the prognosis of above average rainfall, are the SSTs around the continent. They are warmer than average around much of the Australian coastline, particularly to the north and west.
In close to 80pc of years with above average SSTs around continental Australia, rainfall has exceeded normal.
Finally, to the south the Southern Annular Mode index continues to fluctuate from negative to positive but it is becoming more likely it will settle in a near neutral level from this week, helping to increase rainfall in eastern Queensland next week. Generally, a neutral SAM has little influence on Australian rainfall.
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