The weather is expected to turn sharply wetter again after a drier period over the coming 7-10 days for parts of Central and Eastern inland Australia. The main drivers behind this, the shift towards a La Nina developing in the ENSO region, the peak of the negative IOD phase and signals in the longer term guidance for a persistent positive SAM phase into November.
This all drives the rainfall chances up, especially over northern and eastern Australia. And that is where the rainfall bias will continue.
Lets take a look
% chance of exceeding the median rainfall next 6 weeks - October 19th-December 2nd 2021
Not much change from the previous update however the rainfall signals are strengthening as we move into early December for northern and eastern Australia so much of the NT, QLD and NSW will see above average rainfall, NOT ALL, but your chances are running high. Rainfall as we have seen is more uneven in distribution between major rainfall events via showers and thunderstorms. The rainfall bias continues to trend lighter the further west you go through the nation but at this time, most of Australia should see seasonal to above seasonal rainfall values for the coming 6 weeks. The tropics are very active and we will see this play out from this week and throughout the coming period, spreading through WA and down into interior portions of northern Australia.
% chance of exceeding the median temperatures next 6 weeks - October 19th-December 2nd 2021
No change from the previous update. The higher than average rainfall for the north and east will see temperatures begin to moderate after a hot and humid few months. Below average temperatures are likely for the period over eastern NSW west of the divide and through southern inland QLD with the frequent rainfall and thunderstorm events. The SWLD remaining cooler than normal with ridging persisting and the potential for the positive SAM. Seasonal values most elsewhere.
No change to the guidance in the climate models this week, we know the Indian Ocean is negative phase and we are seeing that impact on the overall medium term forecasts with moisture streaming in from the northwest. We are seeing this today as a large cloud band is now descending on the west coast from the Indian Ocean, classing dipole influence, bringing above average rainfall. This influence will continue for the coming 6 weeks across the nation. The SAMA is currently neutral but will trend more positive as we end October and I am of the belief as we go through November, the SAM is likely to be positive, thus increasing rainfall chances along the east coast as you can see in most data sets below. Finally the ENSO which I will speak more about in another post is likely to shift into La Nina during the latter part of November into December, HOWEVER, the shift into the La Nina and the impacts felt in Australia, usually has a lag of about 4-6 weeks and so this is likely to be experienced after Christmas at this stage over the continent. The bigger impacts on that over the north and east.
DATA - Refer to video for more on these sets of data
Euro Rainfall Accumulation Ensemble Data - Next 6 Weeks - October 19th-December 2nd 2021
The wet signal continues as we track through the remainder of October, through November into December. Note the rainfall is increasing each run as we track closer to summertime. The tropics getting warmer, normal. The eastern seaboard getting wetter as well as the easterly winds return, that is also normal. But what is not normal is the rainfall intensity in these regions, with that potentially increasing the flood risks for southeast and eastern Australia. Even rainfall rates running down through the central interior into SA is well above normal and over southern WA, the rainfall is also above average. Much of the nation under the influence of the waning negative IOD, the developing La Nina state in the ENSO and the potential persistent positive SAM. All these climate drivers are forecast to drive above average rainfall, so now we wait to see if this verifies. Confidence is moderate to high on this forecast.
Euro Rainfall Accumulation Control Data - Next 6 Weeks - October 19th-December 2nd 2021
This is the single control member run. Again this will not be the outcome, I am highlighting the increasing rainfall over inland areas of QLD and the NT and through the southeast, which is what I have been pointing out throughout the year. The rainfall increases from November onwards for QLD and the NT, once the wet season gets up and going and through the southeast, the wettest phase is usually now through the end of November into December. Finally, note the rainfall rates over the Coral Sea with those above average SSTs, that is going to be an interesting area to watch in relation to cyclones.
Euro Rainfall Anomalies - Next 6 Weeks - October 19th -December 3rd 2021
That is a VERY WET look or northern Australia with rainfall anomalies 100-200mm above normal for the 6 week period. The rainfall anomalies along the east coast 50-100mm above normal. At this stage most of the nation seeing a 25-50mm increase on normal for this period. Lets wait and see how this verifies.
CFS Rainfall Accumulation Ensemble Data- Next 6 Weeks - October 19th -December 3rd 2021
The east coast wet and this model has really remained unchanged with moderate to heavy falls about. The north probably a little too dry at this stage, but the constant bias of above average rainfall for eastern Australia has been a fixture for the past 2 months and it has verified to a degree. This model now increasing rainfall for outback areas of NSW and into SA. The southwest of WA still remains wet too.
CFS Rainfall Accumulation Control Data- Next 6 Weeks - October 19th-December 3rd 2021
The control member way too dry for the north of the nation and through QLD on current guidance from the climate drivers, but that persistent wet signal for the east coast is the theme on this particular product.
GFS Rainfall Accumulation - Next 5 Weeks - October 19th-November 21st 2021
GFS running a bit drier for the nation west of the east coast. The north seeing an increase in tropical activity which is in good agreement with most models. SA is rather dry so will watch that trend in this particular product in coming days and report back Friday. At this time I am still leaning with the Euro outlook. This run takes us through to mid November.
GFS Rainfall Anomalies - Next 5 Weeks - October 19th - November 21st 2021
Running a little too dry, has the tropics right and the east coast is damp but I do think it will be wetter.
CMC Rainfall Accumulation - Next 4 Weeks - October 15 -November 14 2021
Still a wet look for the month ahead, the end of October with widespread rainfall continuing to increase in the forecasts and we are seeing that appear in the short and medium term forecasts.
CMC Rainfall Anomalies - Next 4 Weeks - October 15 - November 14 2021
Very wet look, and it is increasing each update. The west turning wetter now in the latest outlook for the medium term too. Numbers are coming up over SA and into the NT and northwest. Unlike the GFS, this is picking up on the IOD influence.
CANSIPS Rainfall Anomalies - Next 4 Weeks - October 2021
The wet signal seems well entrenched on this climate model as well, wetter as we go through Spring. Some areas in the green zone over NSW and ACT have seen their monthly rainfall so far. Many areas over the outback of the NT and QLD through northern NSW likely to see rainfall above average during this week coming.
Euro Temperature Anomalies - Next 6 Weeks - October 19th - December 3rd 2021
This is still closest to the post where other models are running too cool or too warm. There is likely to be below average weather for the western interior of WA and through eastern parts of Australia, especially over the coming 3-4 weeks before conditions warm further. The north will be the opposite, running warm for the coming 3-4 weeks before the rainfall returns and starts to bring those heat levels down. Overall this is indicative of a wet and stormy period with inconsistent temperatures throughout the continent and no especially long run of hot or cooler weather for any one area away from the southwest.
GFS Temperature Anomalies - Next 5 Weeks - October 19th -November 21st 2021
The GFS running way too warm in my opinion, and while it is not impossible as nothing is impossible in weather, it is highly unlikely at this time.
CFS Temperature Anomalies - October 2021
Running too cool for the west, but now starting to pick up the impact of humidity on temperatures over the east, while cooler it will be humid and this could still bump temperature above the average during the coming period, especially from mid November.
More details to come on this particular product on Friday.