The monsoon trough is forming once again over the Arafura Sea and is expected to strengthen before it moves southwards this weekend and deepens next week. Widespread showers and thunderstorms turning to areas of rain with heavy falls expected up north.
But the moisture is expected to sweep the nation as the prevailing wind patterns aloft drag that moisture south and east through the nation, providing another chance of above average rainfall across the nation.
The current MJO is turning weak and indiscernible at the moment and will likely result in a low impact from the driver for the moment. But the monsoonal trough is expected to reform regardless north of the nation and bring about a burst of wet and windy weather.
We have got a tropical low on the board expected to form during the coming days but look at the spread below, the guidance is not especially great, which is impacting rainfall for the nation, that is why your totals keep changing.
Potential Tropical Low Tracks
You can see from this graphic below that the placement of the low pressure system is all over the board and the confidence is poor in track, strength and speed. This is why your rainfall forecasts are remaining low confidence nationally and will continue to remain low confidence for those looking further afield.
BoM MJO Forecast - 15th of January - 14th of February 2022
The MJO is expected to remain fairly weak for the coming week but will remerge through the western Indian Ocean at the end of the month if this is right, and come towards Australia during the middle of February. I am not so sure on that. Regardless, the monsoon is set to redevelop across the north and if the MJO happens to return during this period, it may extend the life of the wet spell over northern and eastern Australia.
GFS MJO Forecast - 15th of January - 1st of February 2022
This is probably closer to the truth. Showing the green line going nowhere indicates the MJO is weak and indiscernible through the period into February resulting in no impacts across the north of the nation from the MJO. A trough over the north of the nation may whip up that heavier rainfall guide we are seeing in the forecast packages into the medium term which would then shift south.
RAINFALL DATA - ENSEMBLE FORECASTS
You can see the position of the trough and potential tropical lows plays havoc with the rainfall output from even the broader data sets. The heaviest rainfall is expected with the Euro solution which has the monsoon trough over the north of the nation but a lot of members agree to take the tropical low through northern WA and into Central Australia then onwards to western QLD with widespread moderate to heavy rainfall. The trough over SA this week clearly picking up on the tropical moisture in place and this could be replicated again through the medium term, even though this product does not show it. The GFS and CMC which also run over the same time stamp, very different, and that is in relation to where the tropical low forms during the weekend or next week. The moisture will then run through the nation but the coverage of that rainfall very hard to pin down with any form of accuracy.
Euro 12Z - Rainfall Next 15 days
CMC 12Z - Rainfall Next 15 days
GFS 12Z - Rainfall Next 16 days
With numbers bouncing around it may be confusing, but the take away is, the outlook is looking wet and unsettled for large parts of the north and east of the nation, this will drift south into SA as we can see in the short term and that cycle being repeated a number of times through the remainder of Summer 2022.