THE intensity of the short term heat wave over the south east, which saw temperature records for November fall in many NSW centres, took us all by surprise given that the climatic set-up is now dominated by the Pacific basin La Nina.
However, it serves as a reminder that all assessments for future weather developments must make allowances for the fact that the oceans of the world are now storing more heat than a any time since measurements have been carried out and the warmth of the world's atmosphere is also greater than at any time in recorded history as well.
In the long term, there is some uncertainty how this warmer world will pan out as far as rainfall patterns are concerned.
That is a little unknown at this stage.
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November has been relatively dry in many parts of eastern Australia but the outlook remains for above average rainfalls in many districts over summer and early autumn.
There are a number of reasons for this.
Most importantly, the Pacific Ocean La Nina event is now well established both in the oceans and the atmosphere above them.
In addition, there is a fairly strong polar vortex circling Antarctica at the moment.
As a result, and also to our south, the Southern Annular Mode is generally neutral but it is expected to become positive soon.
Around continental Australia, but especially in the north and east, the sea surface temperatures are up on normal.
Finally, but possibly of considerable importance for a couple of reasons, there is an impending arrival of the Madden-Julian Oscillation pulse in early to mid December.
All these things are expected to aid in bringing increasing moisture over the continent during the summer.
The MJO will possible set a more effective onset of the wet season up north but there is a little doubt about this as it is likely to weaken as it passes the Australian region.
However, it will produce more cloud and therefore the temperatures over the "heat engine" north west of the continent are not as likely to be as high as they have been in recent weeks.
With the La Nina event now favoured to persist into autumn then the potential for reasonable rainfall patterns to persist well into 2021 are reasonably good.
However, good autumn rainfall is also assisted by the development of a negative Indian Ocean Dipole, which is a chance but by no means certain.
In any case, the Pacific is likely to return to neutral by winter with only a low chance of an El Nino before the end of the year.
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