CLIMATE OUTLOOK - SEASONAL AUGUST THROUGH OCTOBER 2021

Headlines


  • Average to above average rainfall for the period of August to October is still likely for large parts of the nation.

  • Average to below average temperatures for the period of August to October still likely for large parts of southern and central parts of the nation.

  • The temperatures to remain above average over the northern third of the nation.

  • Signals for an early build up over northern Australia

  • Signals for a more active storm season for Australia

  • Signals for a bumper August on the ski fields before the snowfall decline rapidly.

Just a note - The wet signal continues for large parts of the nation, however I caution you seeing all that blue on the board, it has to be interpreted against seasonal averages. This part of the world, the deserts and outback, records less than 10mm of rainfall through August and September so it is highly likely these areas would record above average rainfall. Where it is more impressive to see the elevated chances, is in areas that record 50-100mm per month and this is where the above average signals for rainfall sing.


Also with this outlook it does spell out a flood risk for inland parts of the nation through spring, not everywhere but parts of inland Australia should pay attention to forecasts closely over the coming months.


Seasonal Outlook - Rainfall - August to October 2021

The wet signal continues for large parts of the nation with the Indian Ocean Dipole expected to peak during this time. There are also rumblings of the Pacific trending towards a La Nina which would likely form in the November on current guide so not much impact expected from that. So with the main climatic driver during this period being in association with the negative phase of the IOD, rainfall events will continue to be large and widespread, becoming more productive as we see the nation warm up and begin to increase for inland areas of QLD and NSW, as well as through parts of central Australia. This signal has been continuous throughout the past few months for this part of the year and has not changed. There is a likelihood that the negative phase of the IOD will contribute to an early onset of rainfall for northern Australia during this time. Where the long wave troughs set up in the short term forecasting periods will determine where the moisture is utilised, but there is a bias of this being from about central SA through the southern NT eastwards in the global guidance. Confidence in this forecast period is MODERATE.

Seasonal Outlook - Temperatures - August to October 2021

We can already see the impacts of the temperatures being above average under an upper high through northern Australia. This August likely to see elevated temperatures for large parts of the north with higher humidity developing leading to elevated temperatures. This signal starts to wane through September and October, with the chances of rainfall and cloudiness being above average increasing, so bringing those heat values down a tad. Southern parts of the nation still considered to have a normal season temperature wise with those usual spring fluctuations, but if the rainfall outlook verifies and is well above average, then there will be areas of colder than normal seasonal weather overall, the highest chances sitting through parts of NSW and QLD at this time, but this will move around a bit. Bottom line, there is a low risk of anything brutally cold or brutally hot. But these forecasts are always not 100% correct and should be taken as a guide.

MODEL DATA


Euro Seasonal Outlook Rainfall Anomalies- ASO.

The signals from the climate models are largely unchanged, the Euro continuing with the Indian Ocean strengthening, bringing more moisture and rainfall through the nation from the northwest, but it could be that the frontal weather could be parked a little further east, hence why rainfall totals are not above average or signaled to be well above average over with the moisture being utilised over SA, VIC, NSW and QLD. The possibility of a weak La Nina developing over the Pacific also enhancing rainfall chances for northern Australia and introducing early onset rainfall through October.

CFS Seasonal Outlook Rainfall Anomalies - ASO.

A very wet signal from the Climate Forecast System, showing that fully realised negative IOD with copious moisture streaming across the nation with lower air pressure available. Pockets over northern and eastern Australia may be drier than normal but seeing that 2 of the 3 months are in dry season, it is really nothing write home about, the anomalies sitting just offshore northern Australia, lots of blue on the board suggests that the early onset wet season may be on. If that occurs, that will enhance rainfall for southern and eastern states as that moisture feeds into inland troughs and slack pressure pattern keeping rainfall events active for longer, and enhancing the storm outbreaks over the eastern parts of the nation.

CANSIPS Seasonal Outlook Rainfall Anomalies - ASO.

Less resolution in this model with less data sets but showing the possibility that the early onset rainfall may be more acute earlier in Septemnber, but will watch trends. A drier signal for SA and WA is lower confidence, under the current climatic drivers, these areas should see a higher chance of achieving at least average rainfall. So this is the least likely solution, but generally, there is good consensus for widespread rainfall across the nation increasing the chance of atleast average spring rainfall, many areas above average rainfall.

CFS Seasonal Outlook Temperature Anomalies - ASO.

A colder signal for many parts of the nation with a higher chance of many areas through the coming 3 months being below average. I am not so convinced on that idea given the current observations. I am thinking that the warmer air will be further south with the potential early build up. If there is extensive rainfall as per the CFS rainfall outlook then most certainly a colder three months than normal can be verified, but I would think it would be a little warmer than this.

Euro Seasonal Outlook Temperature Anomalies - ASO.

I think the Euro is a little closer to the post with the temperature outlook for the season ahead. The warmer start to the season during August will likely lift these values over northern Australia. The average to slightly below average temperatures elsewhere, in line with the above average rainfall signals.

CANSIPS Seasonal Outlook Temperature Anomalies - ASO.

Similar to the Euro, the warmer than average end to July and into August will help propel the warmer signal over the northern parts of Australia before the early onset rainfall commences. Widespread average to above average rainfall through the season will keep temperatures seasonal.

I will have more on the state of the climate next week with a 2 week forecast on Monday and another climate update for August on Tuesday.

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