BOM has shifted it sights to October to December being the period of above average rainfall, despite also saying rising temperature over Antarctica could result in below average rainfall.
The Bureau of Meteorology's computer generated map (above) shows the 75 per cent chance of rain for the three month period.
BOM climate operations manager Dr Andrew Watkins said the 2020 Spring Outlook was being largely driven by changes in sea surface temperatures in the tropical Pacific and Indian oceans.
"Most long-range forecasts analysed by the Bureau, including from our own climate model, are indicating a La Nina could develop in the spring, which typically results in above-average winter-spring rainfall for Australia, particularly across eastern, central and northern regions," Dr Watkins said.
"A La Nina also typically brings cooler and cloudier days, more tropical cyclones, and an earlier onset of the first rains of the northern wet season."
Dr Watkins said spring was typically a time of year when outlook models had a higher reliability.
"We're starting to see that in the Pacific with a La Nina beginning to take shape, and we are also seeing some changes in the Indian Ocean, which may also boost the chance of rain during spring."
However, BOM also says record warm temperatures above Antarctica over the coming weeks are likely to result in below-average rainfall across large parts of NSW and southern Queensland.
BOM says the warming began in the last week of August, when temperatures in the stratosphere high above the South Pole began rapidly heating in a phenomenon called "sudden stratospheric warming".
"In the coming weeks the warming is forecast to intensify, and its effects will extend downward to Earth's surface, affecting much of eastern Australia over the coming months," BOM says.
It is predicted to be the strongest Antarctic warming on record, likely to exceed the previous record set in September 2002.
BOM says on Wednesday there is a slight to medium chance of showers, patchy rain, and the chance of a thunderstorm in the southern interior, increasing to a medium to high chance in the southern Maranoa and Warrego districts.
On Thursday, the trough is expected to move slowly across the southern interior, with a slight to medium chance of showers and the chance of a thunderstorm in the south east.
Meanwhile, tropical cyclone outlooks will resume on November 1.