CLIMATE UPDATE - WINTER INTO EARLY SPRING.

HEADLINES


  • Strengthening signal for above average rainfall connected to the warming Indian Ocean.

  • Strengthening signal for near seasonal temperature values over southern 2/3rd of the nation but a warmer signal over northern Australia with increased humidity values through the dry.

  • A wet start to spring also likely with a slow warming trend to the summer season.

  • Early onset rainfall possible for northern Australia this year.

Current Forecast Analysis


Rainfall for July through September 2021 - Valid June 16th 2021.

Higher values of above average rainfall though impressive in picture is not that hard to achieve through the deserts of Australia. Though rainfall anomalies are favouring a wet spell thanks to the Indian Ocean, the forecast accuracy is low to moderate where we have to monitor the overall development of the IOD and how other climatic drivers work with this phase, especially the Southern Annular Mode (SAM).

Temperature Outlook for July through September 2021 - Valid June 16th 2021.

CLIMATE DRIVERS

SAM - Currently NEUTRAL but there is no skill in being able to forecast this climatic driver well ahead of time and so refer to shorter term forecasting where I will mention this further, but it does play a huge part in rainfall distribution throughout the remainder of winter into Spring.

Current SAM Forecast for the coming 2 weeks - Valid June 16th 2021.


Indian Ocean - Expected to be called NEGATIVE in phase by most models through winter and into early spring. This will increase the run of northwest cloud bands (one we can see today and again next week) The latest model spread which is far and wide, all point to a deepening negative phase which could strengthen through spring and not resolve until December which would see a wet 6 months coming for much of inland Australia.


ENSO - Currently NEUTRAL and likely to stay in this phase for the remainder of the year. Some climate models want to shift it close to another La Nina, but I am siding with conservative forecasting which is suggesting a neutral phase for the present time.


MODEL DATA

Rainfall Anomalies - EURO Climate Model.


Seasonal Outlook - July through September 2021

That strengthening negative phase in the Indian Ocean will dominate the development of inland rainfall events across Australia with large cloud bands likely to form, we have seen them in recent weeks and we will see further events, with these producing widespread rainfall rather than the inactive cloud bands of late. Some parts of southwest Victoria and the west could see spells of drier conditions through this period, but rainfall will still be about and this is conditional on the SAM being neutral and or positive.

Seasonal Outlook - August through October 2021

A sharp strengthening in rainfall signals will likely to take place as we see the nation warm up as spring develops over Australia. Early onset rainfall also a chance as we track the moisture through to more unstable hotter airmass over the nation where lower air pressure forms in response to the heat building. Over the nations central and eastern interior, widespread rainfall will likely continue through the late winter into early spring, then turn quite thundery as conditions warm up. The storm season could be quite active again this year with all modes of severe weather possible, but heavy rainfall leading to flooding would be the main concern for those over NSW and QLD.

Seasonal Outlook - September to November 2021

The signal for above average rainfall begins to simmer down through the back half of spring and starts to escalate over QLD and possibly the southeast of NSW but more likely over QLD with the beginning of the wet season proper from November. Early season wet weather likely to extend right over northern Australia. Wetter than normal signals begin to broaden in response to the seasonal shift, the IOD will begin to weaken during the middle of spring with the ocean temperatures responding to the seasons changing.

Seasonal Outlook - October through December 2021

The wet signal continues over QLD with widespread rainfall with increased cloudiness with higher humidity values in response to the warmer SSTs over the months preceding this time. A wet look will likely continue into December, but the rainfall will be transitioning into more convective rainfall, so more thunderstorm outbreaks connected to troughs of low pressure which are always quite productive, if you are on the right side of them.

Temperature Anomalies - EURO Climate Model.


Seasonal Outlook - July through September 2021

Near normal values for the coming winter through much of Australia, though as we have seen there can be pockets of well below average temperatures, which we have observed in recent months despite the signals being warmer than normal in the short and medium term deterministic and ensemble data. The climate models do trend with an average season though warmer than normal weather will likely develop over northern Australia in line with the negative IOD increasing humidity values and bringing a shorter dry season to the region. The impacts will be felt from August onwards.

Seasonal Outlook - August to October 2021

With the IOD strengthening and temperatures starting to increase over northern Australia, the warmer start to the wet season with well above average humidity values will bring an early build up and early onset of rainfall. That rainfall, if extensive enough my bring cooler than normal conditions to parts of the north. Neutral conditions, neither a bias for above and or below values for much of Australia with the IOD in full swing, allowing for days of rainy cloudy cold weather, but assisting in milder air being drawn across the mainland too ahead of frontal weather or troughs.

Seasonal Outlook - September through November 2021

Temperatures looks nearing seasonal for the period, with perhaps a soupy build up over the NT and WA bringing up the day time temperature averages a fraction overall but it will be marginal in that it will just be a filthy early build up. That will send more humidity to the south and east and perhaps periods of above average temperatures can be expected throughout the region. There is no strong signal for this however so probably more accuracy and specifics as we go through the winter.

Seasonal Outlook - October through December 2021

Very similar to the above where the accuracy and specifics will likely become clearer and more advanced as we get closer but for now it is looking seasonal with regular rainfall and I dare say a soupy nation.

The current trend for a wet 6 months is looking more likely as we update through the seasonal data sets coming out. The climate models are all pinging a very similar look but as always look to the short term forecasts and medium term analysis that is on here near daily to verify how these longer term outlooks perform. This is raw data analysis and should be treated with caution due to the inconsistency we have seen in previous years under similar circumstances.


Need more information for your part of the world about the state of climate? Email me at karllijnders@weathermatters.org for more information about how I can curate a forecast for you.


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