SA - CLIMATE - AUGUST OUTLOOK WITH A PEEK INTO SEPTEMBER

Headlines


  • A bias towards a wetter and warmer August, with the weather trending wetter and warmer as we go through the month.

  • Temperatures rising over the coming fortnight ahead of the next batch of wet weather for the second half of the month.

  • The trend continues in the modelling for the weather to get warmer and then wetter as we travel through August, so there has been little change in the data sets. We have already had a taste of early spring conditions over the weekend and early this week, that will feature again through the month.


But the impact those elevated temperatures have had on weather systems coming out of the west, even though not as robust as previous weeks, still kicked off widespread rainfall again last night.


The negative IOD continuing to be in a negative phase and deepening also having a large impact on the wet signal coming up over four weeks and indeed into September.


The wet signal does intensify through September and October hand in hand with the temperatures rising over northern Australia and that heat then spreading southwards with the seasonal shift. The warmer the air, the more moisture it can hold. So the more robust the rainfall events become over the next few months


Finally, the rainfall as it does become heavier and more thundery, could lead to pockets of flooding over inland areas. This will see some areas of the outback cut off, communities could also be cut off.


IF YOU LIVE IN A FLOOD PRONE LOCATION - NOW IS THE TIME TO PREPARE FOR FLOODING TO OCCUR THIS SPRING. THIS DOES NOT MEAN IT IS GOING TO FLOOD, BUT THE RISK IS ELEVATED!


Rainfall Outlook for August

% chance of deviating from the median August rainfall.

Temperature Outlook for August

% chance of deviating from the median August temperatures

Euro 12z - M - Rainfall Anomalies for August 2021.

The models continue to ping above average rainfall for larger parts of the nation with the Indian Ocean Dipole the main driver in this. The humidity should begin to increase for northern and eastern Australia next week as the westerly wind belt starts to move south. There is still an expectation for the moisture to build substantially over the coming week or so over northern, eastern and western parts of the nation. We now wait and see whether upper troughs or cold fronts can lift that moisture. The longer it builds, the deeper the moisture profile becomes. There is a higher chance of seeing high pressure settle over the southern parts of the nation, keeping things dry there for a decent period next week. IF that occurs, that will see easterly winds return to the east, bringing showers back to QLD and NSW. That moisture then being drawn over the inland. The NT and north QLD and WA will notice the comfort levels decrease. The weather may give rise to morning showers and possibly a few thunderstorms popping up over the northern parts as winds veer northeast. This moisture also dragged south during mid month. The final area of moisture and rainfall will be derived from the Indian Ocean through WA and this moisture most likely to link into cold fronts as they move through southern parts of the nation. This will be a recurring theme during August and September once we see the pattern flip again, the high pressure over the southeast moving away and frontal weather returning.

Euro 12z - M - Rainfall expected for August 2021.

This is the average across 50 data sets from overnight and it is getting wetter each time these data sets update. Again there are some members that are much wetter for the eastern and southern inland, though a handful are drier than the average. But the bias is for a wetter signal to increase through the month. We can see that likely to play out as we watch the build up to that taking place, moisture increasing in a warming continent during the coming 10 days. We must see that first before this forecast begins to verify.

CMC 12z - M - Rainfall Anomalies for August 2021.

CMC also shows a wet signal for the nation, but in line with the guidance, wetter as we go. This model had picked the rainfall well for WA and SA last month and the drier anomalies over SA in June so it has performed well in recent months. Again the rule of thumb, the warmer the nation gets, the more moisture the atmosphere can retain and then transport south in northwest to westerly winds. Also note that we can have large scale cold fronts interact with these warm moist airmasses, and one system alone can deliver 1-2 months rainfall if the ingredients come together.

CMC 12z - M - Rainfall expected for August 2021.

Rainfall becoming widespread over the nation, again as we go through the month. This period coming up from now until mid month will be quiet with low rainfall and that is to be expected after a vigorous period of weather. The rainfall does not need to be heavy over the outback to exceed the rainfall average for August but these numbers being printed out below are quite excessive if they verify. August is a drier month for much of the nation.

Euro 12z - M - Temperature Anomalies for August 2021.

A warmer trend developing over the next week with the westerly winds starting to retreat and high pressure taking over. The models are split on how much of an influence the westerly wind belt will have on the temperatures over the coming few weeks, but the Euro has performed by and far above the other data coming in and it is suggesting that the westerly wind belt will moderate over the coming 2-3 weeks. That doesn't mean we won't see fronts, they just are unlikely to surge northeast and bring blasts of dry cold air through the nation, hence why you see the moisture building up over inland portions. So for now I am keeping the temperatures above average for most all states away from the coastal areas over the south. That said again, the quicker we get to the above average temperatures, the quicker we see the rainfall develop over the inland areas of the nation.

CMC 12z - M - Temperature Anomalies for August 2021.

Here is an example of not only a wetter signal for the nation impacting temperatures but more frontal weather developing through the latter part of the month, seeing thick cloud cover develop over the nation. So this is where we see the differences in the modelling moving forward. But again, warming as we go through the coming weeks. That will then lead to the moisture over the inland becoming more utilised, via troughs that may form in the heat over the north and eastern inland.

Euro 12z - M - Rainfall Anomalies for September through October 2021.

It may not be pasted in blues and green but for the wettest time of the yea for southeastern parts of Australia, those are robust anomalies for large parts of the VIC and NSW. With these areas already in flood warning and watch regularly, this could be an area of concern for spring flooding, also combining that with snowmelt. For northern parts of the nation, an early build up is highly likely with scattered showers already developing for some locations during next week. The moisture then throughout the nation will likely increase further during September with the afternoon convective weather becoming more scattered over the north, allowing the moisture to then build up over large parts of the inland. Using that rule about the warmer the air, the more moisture it holds, coming into storm season over QLD, NSW and VIC, the storm season could be very productive rainfall producers. Humidity values also likely to be above average for large areas so again this impacts producers and crops as well. The tap may be turned on for some areas and not be turned off for a while. So it could be from famine to feast in some areas in terms of rainfall.

Euro 12z - M - Temperature Anomalies for September through October 2021.

Temperatures likely to be above average for large parts of the nation in August into early September, but with the elevated chances of rainfall and increased cloud cover, the temperatures for inland areas of the nation may moderate further in September and possibly move below average in some parts of NSW and QLD. That is conditional and based upon the rainfall frequency, intensity and duration over the eastern inland as that is a hard ask with elevated temperatures over the north and an early build up as well as above average SSTs around the nation. But the north will have a disgusting September it would seem with the dry season a thing of the past. Most elsewhere likely to see seasonal weather conditions in terms of temperatures, but the humidity could be elevated.

I will have a climate drivers update on Friday for the nation




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