ALTHOUGH the Southern Annular Mode has become slightly positive in the last couple of weeks, the Southern Ocean westerlies are sufficiently dominating to keep the subtropical high pressure ridge well to the north across continental Australia.
This is resulting in a continuation of very dry air over most of south-east Australia, apart from southern Victoria and Tasmania where cool westerlies are bringing periodic moisture.
Further north it is directing bursts of very hot dry air towards the east coast, especially in Queensland and northern NSW.
This is the synoptic pattern that has been dominant for some weeks and it needs to break down significantly before we can return to a more normal spring rainfall pattern.
There are some indicators that imply this is increasingly likely especially from mid spring.
The eastern tropical Pacific continues to cool and more models are starting to indicate that a weak La Nina could be in place by December.
Although the La Nina set up is usually good for rainfall in eastern Australia in summer, late developing La Nina events, such as this one, have not always resulted in good summer rains but more variable falls.
The Southern Oscillation Index (SOI) remains in the neutral range but towards the positive (La Nina) end while the south-east trade winds in the tropical western Pacific remain a little stronger than average – both these features are signs of a potential La Nina developing.
The Indian Ocean Dipole (IOD) is near zero and favoured to remain there for a while.
So all this means a warmer than normal spring and above average temperatures are likely to persist into summer but temperatures will be closer to normal than spring.
Rainfall potential remains low for a while but later in spring and summer, at least average rainfall is favoured in the north-east half of the state.
Severe storm potential in November and December especially is a little higher than normal this year.
Sunshine hours and evaporation levels will also remain above normal in the coming weeks.
