Plenty of interest as we close in on the beginning of harvest and the main issue, is rainfall, how much, when etc. These questions can be answered broadly, as many of you understand, there is no skill in forecasting that far ahead. But we can look together at the guidance ahead and there is a theme this Harvest - that it looks wetter than normal for many areas, not all, but many will be dealing with significant rainfall.
Lets take a look.
Rainfall Next 6 Weeks - September 21-November 5 2021
%chance of exceeding median rainfall for the coming 6 weeks
The guidance is largely unchanged from last Friday where we have a wetter bias over the Murray Darling Basin with rainfall frequency increasing through the coming few weeks in line with the seasonal shift. The weather over the southwest of the nation looks wetter than normal in the short two weeks and this may decrease as we go into October with the SAM trending positive and allowing rainfall to build up over the eastern states. The tropics will become humid with widespread showers and thunderstorms redeveloping as the build up gets underway. That early season activity is anticipated the increase rainfall chances for central and eastern inland parts of the nation as well, some of this may drift into SA but a lot of it tends to divert into eastern Australia so even though that most modelling supports rainfall coming back into SA, it is more often than not that the wetter weather will be further east through this period over VIC, NSW and developing through QLD.
Temperatures Next 6 Weeks - September 21-November 5 2021
%chance of exceeding median temperatures for the coming 6 weeks
No real change in the guidance in terms of temperatures with seasonal values overall for much of the south and southeast. Warmer bias continues over the north of the nation with higher humidity values expected for this time of year, elevating the heat levels and bringing up the day time and night time temperatures. Rainfall events of a higher frequency over southern and eastern parts of the nation will offset any warmer bursts between rainfall events rendering this period seasonal to below seasonal still.
SOUTHERN ANNULAR MODE - SAM - TRENDING POSTIIVE
The Southern Annular Mode is anticipated to turn positive over the coming week which will aid increasing rainfall chances for eastern Australia, with storms and rainfall breaking out along troughs. We can see that in the short and medium term. The SAM then turns into a split camp as you can see into the second week of October, this split camp expresses uncertainty and we want to see that to become tightly clustered in future updates to improve the forecast confidence in the rainfall and temperature guidance.
INDIAN OCEAN - NEGATIVE
Despite the modelling from the BoM saying the event is over, I am again going with the International agencies which support the negative phase gathering pace, strengthening through October and peaking later next month and easing through November before it concludes in December. That will add moisture into the air and be fed by the jet stream and feed inland troughs and heat lows that begin to form.
ENSO - NEUTRAL FOR NOW.
This driver is anticipated to have a crack at turning La Nina, but it will have little impact through this period but for those that are getting crop off in November through December, pay attention to this driver and further updates in the coming weeks as the decision will be made to call the event in the coming 6 weeks either way.
DATA SETS - Refer to the video for more details.
Euro 12z - Rainfall for the next 6 weeks - Ensemble Data
Wetter as we go through Spring as outlined in previous forecasts.
Still shot for you to review. Again wetter as we go through Spring - the air gets warmer, the moisture it is able to hold, the more productive the rainfall events become.
AREA TO WATCH - FLOODING IS POSSIBLE ABOUT THE SOUTHEAST AND EASTERN INLAND OF NSW AND VICTORIA IF THIS VERFIFIES!
Out west, the rainfall is near seasonal for this time of year as the rainfall frequency decreases, but when it rains, it could be heavier with higher moisture content in the atmosphere this Spring.
Euro 12z - Rainfall for the next 6 weeks - Control data
CFS 12z - Rainfall for the next 6 weeks - Ensemble data
CFS 12z - Rainfall for the next 6 weeks - Control data - AREA TO WATCH.
Strengthening signals for well above average rainfall in the east, will review this again on Friday.
CFS also very similar as per the Euro dropping off the rainfall frequency over the SWLD of WA. Rainfall comes back to the north and interior in line with seasonal expectations and shift to the wet.
Euro 12z - Temperatures for the next 6 weeks
Temperatures again are a roller coaster ride with the Euro closest to the post.
CFS 12z - Temperatures for the next 6 weeks
The CFS suggests much colder conditions still and has been persistent in this idea, will keep watch of this.
I will have further updates on Harvest 2021 on Friday when the latest data feed comes in Thursday and Friday but there are increased chances of heavy rainfall for areas that don't want it at the time of harvest! The higher risk resides over VIC, NSW and QLD at this time, lesser risk for SA.