MEDIUM TERM FORECAST AND A BRIEF LOOK INTO OCTOBER

Many people have been drenched, many areas have missed out again, and we have all experienced quite a spike in temperatures this past week, leading some to fear we are set to bake through Spring and Summer with no rainfall. Let's get down to what the data states and see if I can answer some questions for you.


Rainfall for the this week - September 5-12 2021.

Rainfall quite lean this week, as forecast last week, high pressure coming in and that will see a fairly quiet benign week of weather. Trade winds over the FNQ coast will bring in the moisture through northern areas of the nation with showers remaining on the eastern coast of QLD and the Top End. Then a weaker front/trough will bring in patchy rainfall for SWLD of WA with light falls, the better rainfall with that trough expected through western Tasmania.

Rainfall for the following week - September 13-20 2021

High pressure continues to linger through the second week of the outlook, however the drier air is likely to be overrun through northern areas of the nation with a risk of showers and thunderstorms returning to the NT and north of QLD. Showers may develop for parts of the central interior and through the eastern inland with another shot of moisture coming down ahead of a trough, that likely bringing the next chance of rainfall for the south and east of the nation. Out west, there may be another impulse of moisture with showers increasing through this period over SWLD. Otherwise dry weather for much of the western and central interior.

Rainfall anomalies - next 2 weeks

Likely to be quiet and this is expected to be reflected in the rainfall anomalies for this period. This is not uncommon after such a large rainfall event over much of the nation. The high pressure belt over the south to dominate this week and likely to be in place for part of the second week as well, leading to a lot of brown on this map. However many areas in the east and north have recorded well and truly above average rainfall for the month so far which is pleasing. The next major rainfall event is not anticipated until the second half of the month at this time, but in Spring, these things can change rapidly, but on current guide it is looking quiet.

Temperatures Anomalies for the next week

Below average temperatures over much of the south and east of the nation today with a surge of southerly winds moving north with drier air, the weather is expected to remain cooler than average for many areas, frosts are a risk in response to this over the next few days in the south and east. The weather will warm to seasonal and then above seasonal values from mid week onwards for most of the south and east, as the high takes a journey into the Tasman. A milder change passing through WA will slide southeast bringing marginally cooler weather. The northern tropics, dry out but heat levels are still above average.

Temperature Anomalies for the following week.

The above average temperatures likely to continue for the first half of this period with a high likely to be in control with multiple centres over the east and the south. It is unlikely that heat values will get as high as this week gone, but will watch. The weather over the west may turn cooler with a stronger front passing through with that feature likely to run across the nation bringing cooler weather with it. The north is expected to remain hot and becoming humid once again as the build up edges closer with heat levels well above normal.

DATA SETS


18Z GFS - Surface Pressure Pattern next 2 weeks

The pressure pattern is much quieter with a dominance of high pressure and drier air combining for a drier week this week, with the rainfall chances starting to pick up as you can see in the second week, over the north and northeast.

18Z GFS - Precipitable Water Values next 2 weeks

You can clearly see the dry air surging north today through the nation with the colder shift continuing to march northwards with below average temperatures. The air being dry under high pressure will lead to clear skies and lack of rainfall events in the coming 7-10 days.

18Z GFS - Rainfall for the next 2 weeks

And really after today, not a lot, some rainfall returns to the southwest of the nation with a cloud band with patchy rainfall in the SWLD mid to late week, that then sweeps into TAS thanks to a kick along from a weak cold front, that may bring a few showers into the southeast next weekend, otherwise the FNQ will be damp thanks to trade winds. The humidity picks up in the following week with showers and storms returning and it is from that moisture we will see rainfall chances increase over the nation.

12Z Euro - Rainfall Anomalies next 2 weeks

12Z CMC - Rainfall Anomalies next 2 weeks

18Z GFS - Rainfall Anomalies next 2 weeks

12Z Euro - Temperature Anomalies next 2 weeks

12Z GFS - Temperature Anomalies next 2 weeks

A LOOK INTO LATER SEPTEMBER AND THROUGH TO MID OCTOBER.

The weather is expected as per the climatological expectations, to turn wetter through the latter half of September and indeed into October as the tropics wake up and the nations warms up. We have seen a preview over the eastern and southern parts of the nation this weekend, with the warmer the air, the moisture it can hold therefore producing more rainfall. And we saw that play out.


That will be the case for the latter half of September, with another similar rainfall event more likely that not to break out over the nation, again it could hit the same areas as per this system concluding, or it come through SA and NT. It is too early to say, but the weather patterns do lend itself to turning wetter for the back half of September into October.


Temperatures look to remain above average over the north for the coming 6 weeks at least, which will be drawn southeast and south through the coming period, it is expected to warm up - as expected. It is now just a measure of whether the moisture gets drawn into this warmer shift to produce the heavier rainfall events when lifting mechanisms are in play.


Euro Longer Range Rainfall - Next 6 weeks. 51 MEMBER DATA SET - THIS IS THE AVERAGE/MEAN.

You can see the system that has moved through the south and central areas but watch how the rainfall chances pick up through the month and into October with this model (usually reliable and picked the flood events for NSW and QLD over the years as one example well in advance) conservative in it's approach showing some fairly solid rainfall accumulation through this period. Remember you can get one event that drops way more than what is advertised, as has been the experience this weekend.

Euro Rainfall Anomalies - Next 6 weeks

Euro Temperature Anomalies - Next 6 weeks.

I will have a full climate update for the remainder of September and my first charts looking at October on Tuesday.


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