LATEST RAINFALL UPDATE. WHEN THE MONSOON ARRIVES - THE MODELS GO MAD.

There are growing signals for the monsoon to return to northern Australia throughout the medium term which is playing havoc with the rainfall forecasts and will continue to play havoc with the rainfall forecasts, as some have the major impulse of tropical moisture going into the Pacific, some have it running over the NT and others into the Indian Ocean. All of these making it hard to pin down which model you go with.


So your apps, your data beyond about 7 days will remain very low confidence and lead to wild fluctuations.


Lets take a look


SHORT TERM

The showers and thunderstorms which is driving the rainfall distribution will continue for a number of days through the southeast and east of the nation as well as the tropics as troughs move through a deep moist airmass. The rainfall random and scattered and so some areas copping it and other areas seeing not much at all. The weather over southern and western parts of the nation will remain dry and settled closer to the ridge. The tropical rainfall will begin to increase over the weekend if not next week as the troughs and tropical waves lift the moisture into widespread and linger longer, dropping temperatures.


UKMET - Rainfall Next 7 Days - MODERATE CHANCE

The weather unchanged in the short term but will be watching that mid level trough this weekend into next week for SA. Dry out west is a fair call for now.

MEDIUM TERM

Every model below carries a low confidence due to the monsoonal potential. Refer to the notes under each model for more.


ICON - Rainfall Next 8 Days

Starting to pick up the mid level trough next week for SA and the NT but too dry for QLD.

CMC - Rainfall Next 10 Days

Uneven distribution of rainfall for the period, thanks to the deeper moisture spreading throughout the nation. Does not see the monsoonal flow developing as it did yesterday. Has another rainfall event for the east next week.

EURO - Rainfall Next 10 Days

This is likely the correct solution for now. Has the storm outbreak for the southeast tomorrow and then the east next week. The tropical weather increases over the weekend and next week with heavier moisture levels over Indonesia approaching for the mid month period onwards over northern Australia. The west is trending drier in forecasts and I may need to adjust my forecasts tomorrow to reflect this.

ACCESS - Rainfall Next 10 Days

This is also a very plausible solution relating to the rainfall event potential next week over the east and southeast. Mid level trough this weekend deepens next week before passing into the eastern states. The tropical weather increasing as well thanks to the monsoonal weather approaching Australian waters. This is quicker in bringing the moisture south.

KMA - Rainfall Next 12 Days

This is in line with the ACCESS so will take a look at this tomorrow morning to see how it verifies, but this would increase flooding for NSW and QLD once again. Monsoonal weather is creeping south into the Indian Ocean.

GFS - Rainfall Next 16 Days

This like the ACCESS and KMA, brings the monsoonal weather in quicker than other models, and the impact would be significant. Will review this during the morning and with the tropical updates to come through the next week (look out for those). The east unstable in onshore winds.

ENSEMBLE DATA

This will prove to be more useful for the medium term as opposed to the staple data sets that many of you use. The broader data sets carry more detail and higher confidence with a bigger data set underpinning the forecasts.


GFS - Rainfall Next 16 Days (median of 35 members)

This is the most unlikely outcome from the model sets tonight with the ensemble data drier than the deterministic. That expresses a high degree of uncertainty that needs to be worked out over the next week or so.

CMC - Rainfall Next 15 Days (median of 30 members)

I am leaning more with this solution in terms of coverage of rainfall moving forward over the course of the next 2 weeks. The tropics very likely to see an increase in rainfall and that will increase rainfall down the line for most other states and territories. But you can start to see that seasonal shift to the wet season.

EURO - Rainfall Next 15 Days (median of 51 members)

The tropical weather up north is looking quite intense on the ensemble data vs the deterministic above, which suggests more uncertainty but if the monsoon does arrive, the impacts as mentioned would be above average rainfall, high chance of early cyclone activity in all waters. If that happens then the rainfall numbers for southeast and southern Australia would be elevated higher than this.

LONG TERM

This remains unchanged, the very wet signal remaining stubborn for the remainder of the year and into 2022.


GFS - Rainfall Next 5 Weeks

The GFS is very keen on entrenching that monsoonal flow over the north and you take the time line out a few more weeks and the impact nationally could be dire for those floods zones in the east and southeast.

More tomorrow from 7am EDT.

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