We are inching closer to many people starting to get ready for harvest, especially in zones expected to see a lot of rainfall in the coming week. This may cause a few headaches with the rainfall not expected to be light and patchy, rather, with thunderstorms in the mix, some areas could see a month's worth of rainfall in the space of a day this week. The rainfall will be uneven in distribution so be aware of that when looking at all rainfall forecasts.
Now to the longer term.
% chance of exceeding the median rainfall for the coming 6 weeks. September 28-November 12 2021
No real change to the forecast from last Friday, but we are seeing a sign of what is to come this season, heavy rainfall this week, deepening low pressure troughs and severe storms on the board for a number of days. Clearly the bullseye of heavy rainfall is NSW with a very high chance of exceeding the September average again before the month is done! After this period, the whole eastern region is about a 70-80% chance of seeing further excessive rainfall events lifting October rainfall above normal, that may come mid month. For the north a very high chance of above average rainfall with the wet season kicking off early. That moisture bringing scattered showers and storms to the outback, all you need is 5mm in some locations and you are above average. Above average rainfall likely for the SWLD thanks to the system coming through later this week. And near seasonal elsewhere.
% chance of exceeding the median temperatures for the coming 6 weeks. September 28-November 12 2021
No real change to the focus of this forecast, the north of the nation with the early build up is expected to see well above average temperatures, we saw Darwin break a record last week for September. The temperature will come down in terms of number but the humidity values are only going up up up. So the above average bias continues there. With the elevated moisture levels, that will contribute to more cloud formation over southern parts of the nation, more rainfall, marginally below average temperatures can be expected for the east. The southwest may continue to be impacted by persistent ridging and southwest or southerly winds.
Rainfall - Remember the rule, wetter as we go through Spring and as the air warms, that means it is able to hold more moisture, that means more productive rainfall events, even IF they are more infrequent.
Euro Ensemble - Rainfall Outlook - Next 6 Weeks
No real change for the coming outlook, there are about 3-4 further rainfall events on the board in the coming outlook period which would support the wetter as we go phase for the nation. The rainfall is turning more convective/warm seasonal so the thunderstorms will become more frequent when low pressure gets involved, we see that from this week.
Rainfall Anomalies for the coming 6 weeks
Very good agreement in the above average rainfall smear over the eastern inland but now starting to see the rainfall anomalies increase over the southern coastline, over the southwest and across the tropics in line with the wetter as we go theme for Spring.
CFS Ensemble - Rainfall Outlook - Next 6 Weeks
This model has been very keen in expressing it's support for the IOD negative phase to peak during the coming 4-6 weeks with rainfall increasing from northwest to southeast across the nation. The upcoming week will give us insights into that. Overall it is an outlier in terms of the heaviness of the rainfall but it is not impossible. Note the tropics getting nice and damp after a few foul weeks of heat.
CMC Ensemble - Rainfall Outlook - Next 4 Weeks
Rainfall in good agreement with other modelling, though this is a little more robust in bringing falls back through to the northwest of the nation supporting the strengthening of the IOD phase.
Rainfall Anomalies for the coming 4 weeks
GFS Ensemble - Rainfall Outlook - Next 5 Weeks
Good agreement with the bias of rainfall over the south and east, the tropics coming alive and the interior largely dry back over to the northwest.
Rainfall Anomalies for the coming 5 weeks - Note the blotchy nature of the anomalies indicating a shift to warm season rainfall, that is convective weather - showers and thunderstorms.
The temperatures are expected to be heavily impacted by the rainfall and cloud cover frequency this Spring and we are starting to see that this week. Also the chance of a colder week for southern Australia IF the SAM turns negative.
Euro Ensemble - Temperature Anomalies - Next 6 Weeks
A slight warm bias over the north and the west and the east seeing near seasonal conditions, that means that after a relatively cooler October, that maybe some warmer and more humid weather developing for the nation into late Spring.
CMC Ensemble - Temperature Anomalies - Next 4 Weeks
The nation would be caked in cloud and rainfall for the coming 4 weeks to see this verify and it is a fair chance going off the latest short and medium term data sets.
CFS Ensemble - Temperature Anomalies - Next 6 Weeks
Mixed odds across the nation reflecting the move to more convective warm season rainfall where we see inland cloud bands and troughs dictating rainfall and spread.
GFS Ensemble - Temperature Anomalies - Next 5 Weeks
Cooler bias over the south and the west with a wet phase unfolding from this week, the model has recently added in a colder shift into the second week of October with a northward surge of the westerly winds over the southeast. Will monitor that trend.
Another update on the Climate Drivers coming on Thursday and this forecast updates again on Friday.