A huge rainfall event is bearing down on Australia with widespread rainfall expected. Western Australia will see the event unfold from Tuesday as tropical moisture from the Indian Ocean streams south and collides into a frontal system. 24 hour totals in excess of 30mm are possible by Wednesday morning over the southern half of WA with plenty hitting the interior. The system will wind up into Thursday as an upper trough, the engine behind strong surface systems, moves east. As it does huge volumes of moisture will be drawn in from the moist northwestern tropics. The result will be more heavy rain for southern parts of WA for Thursday and Friday, clearing the west coast later on Thursday. The meandering low and trough will speed up into the weekend, driving over South Australia and into Victoria by early Saturday. Models are predicting widespread potential for 20 to 40mm over SA and similar for VIC by 10am Saturday. Into Sunday and the rain will push through New South Wales, where more modest totals of 15 to 20mm are expected. Queensland will get its share too with falls above 40mm. The system should clear by Monday or Tuesday leaving a very soggy start to spring in its wake.