The Indian Ocean is shifting seasonally which is normal for this time of year. The weather is expected to be heavily influenced by the Indian Ocean in the coming 6-8 weeks over the nation, especially the western tropics and through the heartland of the nation into the southeast inland of Australia.

And we are already seeing the influence play out on the charts in the coming 2 weeks. This is where we will either see the Indian Ocean verify against the International Modelling suggesting that the influence peaks over the coming two months or against the BoM guidance which says the influence is over.

Time will tell.

18Z GFS - Surface Pressure Pattern - September 23-October 7 2021

The pressure pattern does not look that exciting, but it is showing signs of influence on other parameters. Moisture is streaming south into the Central Basin which is in a good position for influence on spring rainfall come October and November.

18Z GFS - Rainfall next 2 Weeks - September 23-October 7 2021

Clearly the precipitation is beginning to move further south through the Basin which is what you would expect to see at this time of year as the seasonal shift continues to unfold in the coming weeks, moving towards the warmer season. But the rainfall into the Central Basin is highly anomalous and may provide a foundation for further rainfall events into the second week of October, something that I am watching closely while eyes are on the short term modelling looking at the waves of low pressure passing through.

18Z GFS - Rainfall Anomalies - September 23-October 7 2021

Rainfall anomalies as pointed out above is seasonal through the region north and west of Australia, it is normal for the region to be drier, but sitting further afield, in the central basin, where the jet stream will likely help to draw that south and east towards the continent with troughs and fronts running south of this moisture acting as a pulling mechanism.

18Z GFS - Precipitable Water Anomalies - September 23-October 7 2021

And this shows the movement of that moisture south and east into the jet stream lifting rainfall chances over the continent where inland troughs are expected to set up through eastern Australia at this time.

18Z GFS - Precipitable Water - September 23-October 7 2021

This shows the amount of moisture available in the air and you would want to see the warmer tones moving south into low pressure, that low pressure lifting the moisture into areas of rain and thunderstorms. We can see 3 events making impact over WA and points further east through the nation for the coming 2 weeks. So the influence from the IOD is increasing on the current guidance.

Tuesday 28th Of September 2021

Thursday 30th of September 2021

Wednesday October 6th 2021


I showed this yesterday and the remainder of October and November looks damp and cooler than normal with IRI/CPC indicating the influence from the IOD is still expected to be moderate at worst in the coming 2 weeks and again throughout the coming 2 months.

Rainfall Anomalies - October and November 2021

60-70% chance of above average rainfall over large sections of the nation for the coming 8 weeks with a seasonal Spring for much of the west and southwest which would top up the wet winter period. The tropics 80-90% chance of above average rainfall through the coming 8 weeks.

Temperature Anomalies - October and November

Strengthening cooler signal for the coming 8 weeks but this is conditional on the cloud and rainfall forecast verifying above. More rainfall that is observed, the cooler the season will be and vice versa.

I will have an update on the Harvest Outlook tomorrow late morning. Your state based forecasts for the short term coming up after 5pm today.

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