The weather certainly has been very active for the past 6 months over the east, and while we get a small window of drier and more settled Summer weather next week, the coming period offers not much change in the wet and cooler climate bias over northern and eastern Australia.
All the climate drivers are in play to continue the wet phase over much of the nation which is no surprise, we are now at the mercy of the La Nina and the positive SAM phases driving the wet weather. The mitigating factor against this being a nasty 6 week period is the MJO and SAM remains out of phase for wet weather, but the signals are not supportive of this at this time.
So much of what we have seen we can expect to remain a theme for the coming 6 weeks as we round out 2021 and go into 2022.
The one concern that I have with the next week, which will likely set up the next wave of nasty weather to round out the month, is that as the air gets warmer, the more moisture the atmosphere can hold. We have been spared over southeast Australia from the high end flooding thanks to cooler weather, but the cooler weather may be behind us coming up from next week.
The west and central areas may see the hottest weather nationally, but guidance does not suggest dry, and that is thanks to the tropical weather which looks to regroup towards Christmas and into 2022.
Lets take a look
What a significant week of rainfall across the nation, all thanks to the three drivers working together to promote these large scale rain events. The IOD is waning still, but the influence appears to continue for the next week before it is finalised. I was anticipating the influence to wane by now but there is still more moisture being drawn in until mid December through the tropics and an early monsoon in the Pacific is an indicator of La Nina building. The SSTs in the Coral Sea suggest that the La Nina has been underway for some time. The SAM remaining neutral this week but it is turning positive as we edge towards Christmas and into 2022.
The MJO is expected to move into the Coral Sea and Pacific and you will see the development of a tropical low/cyclone in response to that. The MJO then looks to become mobile and race towards Africa, meaning that at that pace it should be in the Maritime Continent during January where rainfall should increase once again. Build up conditions to persist for a while.
DATA - Refer to video for more on these sets of data
Rainfall Outlook - Next 6 Weeks - December 10th 2021 - January 24th 2022
% chance of exceeding the median rainfall for the coming 6 weeks
The rainfall bias continues for the east and north, but now that we are moving into the wet season proper, the ability to get above the 400-500mm monthly averages gets harder for the NT and parts of WA, so that is why the blue shading has gone. In the east, significant rainfall signals continue with heavy falls returning from Christmas onwards into early January, especially southeast NSW and the ACT and surrounds. The west leaning seasonal, some areas below average rainfall is expected as the tropical weather regroups. The nations south and relatively seasonal weather for this period as a whole. Remember in warm season rainfall, thunderstorms generally bring the heavier rainfall in the absence of low pressure systems and broad troughs.
Temperature Outlook Next 6 Weeks - December 10th 2021 - January 24th 2022
% chance of exceeding the median temperatures for the coming 6 weeks
No change to the guidance from earlier in the week. The north will be near seasonal and the west remaining seasonal if not marginally above average with drier weather and clearer skies dominating for the next few weeks. But it is out east that the cooler signal continues, despite the warmer week expected next week. The overall trend of the cool Summer continues.
Humidity Outlook - Next 6 Weeks - December 10th 2021 - January 24th 2022
% chance of exceeding the median humidity for the coming 6 weeks
Thankfully the major monsoonal burst that was being modelled over the nation is expected to remain out in the Coral Sea but the monsoon will return in January. The east under persistent easterly winds are expected to combine with warmer weather to make it feel very tropical in the eastern inland extending back to central Australia. With the La Nina building conditions are expected to become more humid as we go through this period for northern and eastern Australia. The west seeing a drier 6 weeks but the values will continue to increase as we move through Summer as the monsoonal weather moves southwards across the country.
Disease Outlook - Next 6 Weeks - December 10th 2021 - January 24th 2022
The wet weather, and now a shift to hotter weather with high humidity increases the risk of fungal diseases to many crops, even as we enter a quieter week nationally. This signal does not change over the coming 4 weeks. The west may be dry for now, but there will be an increase in humidity returning through this period and with the higher temperatures this could see prolonged periods of above average humidity values as the monsoon deepens and that will have a high impact on crops and produce in the southeast and east of the nation for the end of December into January.
Riverine and Flash Flood Risk January 2022
The fact we have ongoing flooding for much of December as a flow on effect from the high rainfall, additional rainfall will continue to exacerbate this risk through until early 2022. Many inland rivers could be flooded right through Summer 2022. The risk will return for outback areas once the monsoon starts so the back half of the month into early January which will see new areas come under flood risk.
Riverine Flood Risk Summer 2021/22
The flood risk is ongoing and continues through the remainder of December and January, and with the wet signal peaking in February, the flooding is here for a while. Keep up to date with the medium term forecasts in the east as rainfall could return next week and persist again.. The monsoonal weather expected from this week, thankfully has landed east of the nation but the tropics rebound in activity towards Christmas and beyond so that will be of concern to the flood zones over the east and southeast as that moisture moves southeast. Flooding over the west and central parts of the nation will be connected to the tropical lows/cyclones that move around the north.
What a significant week of rainfall across the nation, all thanks to the three drivers working together to promote these large scale rain events. The IOD is waning still, but the influence appears to continue for another 2 weeks. I was anticipating the influence to wane by now but there is still more moisture being drawn in until mid December and an early monsoon could provide a decent amount of moisture as well. The ENSO is the driver that is taking over, with a La Nina phase underway and strengthening in the next 4-6 weeks, likely to peak in January before waning through February. The SSTs in the Coral Sea suggest that the La Nina has been underway for some time, thankfully we have now seen all global agencies including the WMO calling it a La Nina. The SAM remaining positive into early December with brief stint back to neutral values at times, but generally positive of normal is likely.
The MJO has passed through to our north in the past week and is now indiscernable with no impact expected over the Maritime Continent. With a La Nina developing and the waning negative IOD phase, the enhanced moisture, build up conditions will persist and the the likelihood of an early monsoon is gaining momentum as the MJO phase may redevelop by mid December which could assist in enhancing rainfall over the tropical north. There are some signals that it could favour QLD and the Coral Sea.
DATA - Refer to video for more on these sets of data
Euro Rainfall Accumulation Ensemble Data - Next 6 Weeks - December 10th 2021 -January 24th 2022
The models remain unchanged, for the wet signal to build further over northern Australia during this period and over the eastern seaboard. The early monsoonal burst from a few weeks ago lands in the Coral Sea but will likely return in early January. The east is expecting further rainfall and flooding issues as we go through the latter part of this month but more likely in January in line with the monsoon returning and the bulk of the nation looks to record at least seasonal to above seasonal rainfall values.
Euro Rainfall Accumulation Control Data - Next 6 Weeks - December 10th 2021 -January 24th 2022
The heavy rainfall guide continues for the southeast, east and northern parts of the nation with flooding being renewed through January over inland NSW and QLD. Northern Australia will get a good monsoonal burst in January and when that happens, expect rainfall chances to increase nationwide, not just the east. Some areas can expect flooding to develop in areas that have been spared so far, especially over eastern inland areas and through central interior locations. The far south may see seasonal conditions.
Euro Rainfall Anomalies - Next 6 Weeks - December 10th 2021 -January 24th 2022
The numbers over the south and east remain elevated. A slight dry bias for the inland Top End is conditional upon the tropical lows and monsoonal burst, so I override that forecast by treating it as a seasonal 6 weeks for the north. The rest of the nation generally seasonal if you were to take this as the gospel.
The Euro Control Anomalies for the coming 6 weeks shows that tropical weather is the wild card of Summer rainfall and where the tropical lows go is where you find the rainfall. But the persistent excessive rainfall signal for southeast NSW, the ACT and Gippsland of Victoria continues as does the heavy rainfall forecasts for the central QLD coast.
GFS Rainfall Accumulation - Next 5 Weeks - December 10th 2021 -January 12th 2022
Significant rainfall signals continue for eastern Australia and tropical rainfall expected to increase over the coming weeks, with a larger impact on tropical rainfall expected from near Christmas onwards into January. The remainder of the nation relatively seasonal rainfall expected through to early January.
GFS Rainfall Anomalies - Next 5 Weeks - December 10th 2021 -January 12th 2022
The model is now showing a dry bias over the northern and western parts of the nation with the monsoon being analysed over the Pacific Ocean. That remains very low confidence. The high confidence is over the east and southeast of the nation where the rainfall is expected to remain well above normal.
CMC Rainfall Accumulation - Next 4 Weeks - December 10th 2021 - January 10th 2022
Additional rainfall to come over northern and eastern Australia is excessive and this will support further flood potential after the dry week coming up. Watching the tropics closely as we head into Christmas and beyond with tropical weather increasing for the end of the month and into January.
CMC Rainfall Anomalies - Next 4 Weeks - December 10th 2021 - January 10th 2022
The wet phase is easing for a week over the southeast and east but it will return as we get towards Christmas as the moisture profile deepens and the low pressure deepens. So for southeast areas and much of eastern QLD, rainfall will remain above average. Mixed odds for the north with the tropical rainfall still in build up phase but note the first burst of monsoonal weather thankfully has landed in the Coral Sea, that burst would have put the east under the 1/100 year flood risk which has thankfully eased for now.
Euro Temperature Anomalies - Next 6 Weeks - December 10th 2021 -January 24th 2022
The east is looking very much below average with a decent supply of rainfall, cloud cover and this will suppress temperatures. The moisture may return frequently (after this drier period) to bring cloud cover through southern WA and into SA and then the southeast. Certainly are seeing that right now. The tropics seasonal and the west coast is above normal.
GFS Temperature Anomalies - Next 5 Weeks - December 10th 2021 -January 12th 2022
It is persisting with the warmer signal for northern Australia which is interesting, as the other models have been running cooler and the tropics indeed have been running hotter through this season, so certainly merit to this forecast.
December 2021 - Rainfall Anomalies
This has verified quite well so far, and we are seeing that rainfall spread play out from when this data set was released 10 days ago. The wetter signal eases mid month over the east but returns for the end of the month over the north and east. The west, marginally drier, but within tolerance of seasonal expectations.
January 2022 - Rainfall Anomalies
The model has turned a bit drier for January which I am not totally convinced about, the shorter and medium term forecasts support a deepening of the low pressure over the north of the nation, but for now calling it seasonal for the north and west, with drier spots here and there over the outback and possibly through the south, wetter over the east.
February 2022 - Rainfall Anomalies
The wet signal increases over the tropics which is in line with the La Nina in place and the impacts of that being felt from late January into February. The nation as a whole responding to that, with a very wet end to Summer possible.
Summer - Rainfall Anomalies
But looking at the Euro, the impact of La Nina is evident. I would not read too much into that brown shading over WA as it takes one system from the tropics to see that drier bias disappear. The wet Summer continues for the east and north.
More details on the January outlook next week, taking another look at Autumn 2022 for those forward planning before then on Sunday.