Synoptic surface charts over the past week have been dominated by a slow eastward movement of a low-pressure centre which first formed near Carnarvon, Western Australia on September 24.
The low, which was not a strong system, moved across Western Australia and then slowly across the Bight before moving inland across South Australia. Up to this stage, very light rainfalls occurred except for moderate rainfalls around Albany.
As this low crossed western NSW, rainfall continued to be patchy with only light to moderate rainfalls to 9am Wednesday.
The synoptic charts are considered unusual for September, they are more typical for late spring or early summer season.
Maximum temperatures on the Tuesday, September 28 in southern part of the territory just to the north of this low were well above normal.
Tennant Creek recorded 38.8 degrees almost the hottest September day on record in 120 years with dew point temperatures falling to negative values.
This high temperature event at Tennant Creek may have prevented a widespread heavy rain event occurring in both Victoria and NSW. However, the low was showing increasing intensity.
Walgett recorded 59.8mm up to 7.10pm from 9am. This just pipped Walgett's wettest September day of 59.4mm on September 17, 1903.
There was a widespread heavy rain event during the third week of September 1903 and that led to excessive rainfall up to winter of 1904.
Other heavy rainfalls were 43.8mm at Bourke, 40mm at Coonamble and 49mm at Coonabarabran and 43mm at Cowra.
The radar at 3pm Wednesday showed rain echoes over Victoria moving from the east, while further north to well in NSW the echoes moved from the north-west.
Further heavy rain fell Wednesday night in the far north of inland NSW. Moree received 58.8mm, its wettest September day in 142 years of records. Mungindi recorded 58.4mm, its wettest September day since 61.2mm on September 29, 2011. That record fall in 2011 led to a very wet summer and early autumn with floods from Queensland right down to Victoria.
Heavy rain also occurred in the Otways, with Benwarren recording 103.8mm, Mt Sabine, 96mm and Mt Cowley, 123mm, its wettest September day since 1911.
Another low pressure has developed west of Perth and has to date delivered heavier rainfalls to places in southern Western Australia.
This will typically bring more rainfall, perhaps by next weekend.
Unfortunately, an absence of notably warmer than average days for the next fortnight.
Sea surface temperatures south of Western Australia in the western bight region have fallen half to one degree below normal.
An area of below normal sea surface temperature has recently formed in the Pacific Ocean, just south-east of Mackay.
