Although it was expected for some months, it is now official we are in an El Nino pattern and are likely to remain there for at least the now four months.
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The sea surface temperate patterns have indicated an El Nino for some times and recently the atmospheric response has fallen into line.
Trade winds in the tropical western Pacific has finally weakened as to be expected in an El Nino and the 30 day running mean of the Southern Oscillation index of -13 is now well into the El Nino range.
These factors indicate the potential for an extended period for the El Nino which is likely to persist until at least the end of February.
El Nino events typically lead to reduced spring and early summer rainfall for eastern Australia, and warmer days for the southern two-thirds of the country.
In addition, the Indian Ocean Dipole is now positive, and all models indicate that this will persist for another month or two.
A positive IOD also leads to reduced spring rainfall for central and south-east Australia and on occasions when a positive IOD and El Nino occur together, the decrease in rainfall is often stronger and more widespread across Australia.
A positive IOD also reduces cloud cover in the heat engine area of NW Australia increasing the chances of occasional hot spells in the SE states.
To the north, the chance of the Madden-Julian Oscillation strengthening a little and moving into the western Pacific and may increase a little by mid-October, but its effects will be minimal, except in NE Queensland.
To the south, the Southern Annular Mode is currently neutral and little change is forecast to remain so over the coming fortnight.
However, it is not all doom and gloom. In a normal El Nino event, the SSTs decrease in the western Pacific but at the moment there are large areas of warmer than normal water off Australia's east coast.
This means that any period of easterly winds could still see an occasional useful rain event along the east coast at least.
However, this requires a change in the synoptic patterns that have dominated in recent months.
Currently, a significant cold Southern Ocean front is crossing SE Australia, and this has the potential to cause a major change in the synoptic pattern over SE Australia and increasing the chance of more easterly winds.
This could provide a "saving grace" in an otherwise dry and warm end to 2023.
