CLIMATE UPDATE - SEPTEMBER 2021

Headlines


THIS IS A PRELIMINARY LOOK AT SEPTEMBER 2021

  • A warmer month is expected for much of the north with the build up continuing ahead of schedule. With the abundance of moisture, more cloud cover is expected to bring a higher chance of below seasonal temperatures.

  • Cold fronts are likely to drift further south during this month with a trend to more easterly wind dominance. This will also allow temperatures to be near or below normal for much of the nation with cloud cover increasing with higher rates of moisture.

  • Rainfall likely to be near or above normal for most all of the nation, with elevated values expected for the northern tropics and parts of the southeastern inland and pockets of the outback.

  • Rainfall likely to ease over the southwest of the nation though still seasonal expectations is fair at this time.

Rainfall Outlook September 2021

% chance of rainfall deviating from the median for September

The rainfall is expected to pick up in frequency and intensity through September as expected with the climate drivers that are in place. Refer to that here

The month may start out wet with a residual rainfall event spreading from northwest to southeast through the nation active at this time with current projections suggesting an intrusion of moisture coming southeast through the nation from the Indian Ocean. Easterly winds are increasing in frequency through September which is also climatologically expected. With the current guidance from the climate models, they are suggesting that the IOD is expected to play a large part in rainfall increasing across the nation. Three ports of moisture to watch in the coming 6-8 weeks. 1. The easterly winds driving in the moisture from the Pacific and Coral Seas. 2. The Indian Ocean Dipole, moisture streaming northwest to southeast from near Indonesia through WA and into the southeast inland. 3. The tropics are expected to wake up about 4 weeks early with moisture increasing and that moisture also being drawn south through the nation, mainly through QLD and NSW.

Temperature Outlook September 2021

% chance of rainfall deviating from the median for September

Temperatures are expected to moderate through September and depending on the movement of moisture at the end of a warm and humid August, September could start out cooler with thick cloud cover and rainfall ongoing for vast parts of the nation. This will see a mostly seasonal month temperature wise over the southern half of the nation with that increase of cloud cover and rainfall frequency. Where the cooler than normal temperatures are expected is over the eastern inland through NSW and into central inland parts of SA and northern VIC. This area of cooler anomalies may be extended further in coming updates in the next fortnight for September. The build up over the north will see marginally elevated temperatures for the month of September, but it will be the heat levels due to humidity which will be the major impact over northern Australia which will cut the dry season off prematurely.

CLIMATE DRIVERS DASHBOARD

The Indian Ocean is the main driver to bring the most influence for the nation in September but that La Nina risk needs to be watched and an update on that will be up next Tuesday on that once I get the latest data sets from the climate modelling and discuss with my friends at the CPC in the US.

DATA SETS

Euro Outlook - September 2021.

The wetter than normal bias from the Euro continues for the month of September, particularly for the eastern half of the nation. It also has a bias of wetter than normal condition for the northern parts of the NT and extending through the interior into the east as well. Where the model is struggling to recognise that the outback only needs 1-5mm of rainfall in some places to see rainfall anomalies achieved. This is why there is not as much green on this particular chart. However the month will be wetter than normal for many. For most all areas, the rainfall should reach seasonal levels. The SWLD may begin to see a reduction in rainfall as we move away from the wet season in the region.

Euro September Outlook - August through October 2021.

The continuation of the theme of wetter as we go through winter and spring continues to verify in real time and we are now starting to see the wetter signal increase over the eastern and northern parts of the nation spread further west over central and southern Australia. This will see some areas record back to back months of above average rainfall. Some heavier falls are expected for the southeast of NSW, northeast of VIC, through much of southern QLD, much of northern Australia and a better than 50% chance of above average rainfall for most of the nation. The SWLD land division of WA even though we are moving out of the wet season, there are still signals for lingering rainfall in the spring time.

CANSIPS Outlook - August through October 2021.

The model resolution is not as high as other agencies, however the message is the same, as we go through this month and into September, the weather trends more humid, wetter and thundery over northern and eastern Australia, which then spreads west through central and southern Australia through September into October as the IOD peaks mid to late spring. The wet signal could be quite aggressive for the NT which is normal under the current climatic drivers.

CFS Outlook - August through October 2021.

The Climate Forecast System does show how some of the members that contribute to the ensemble data may look for the month, with pockets getting absolutely drenched while others scrape together near normal rainfall. I am not aligning with this particular agency, but just showing the other solutions on the table. I do not agree that the north will be drier than normal for this seasonal outlook.

Euro Temperature Outlook - September 2021

That warmer signal continues over the north but it is starting to wane from the August values and what is being experienced now. The cooler signal starts to emerge over the eastern inland which is in line with the main driver the Indian Ocean Dipole bringing increased cloud cover and widespread rainfall. This forecast is conditional upon those elements verifying and I would be expecting the next 2-3 weeks will be crucial in seeing whether we do see the cooler signal for the south verify as the models do indicate.

CANSIPS Temperature Outlook - September 2021

Very good agreement again with the warmer signal for the north and the seasonal to below seasonal temperatures for inland areas and along the south and eastern areas in line with the rainfall frequency increasing.

CFS Temperature Outlook - September 2021

This is probably a little too aggressive, not impossible but it would be a very wet period if this was to occur, or there would have to be the return of the cold front barrage. I am not aligning with this outlook but it is never impossible, just a very low chance of occurring.

I will have an August Update on Friday to see what the rest of the month looks like and next week look out for the Major Update on Climate Drivers and in particular the La Nina potential.

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