The head of Nasa's balloon programme, Debbie Fairbrother, said meteorologists would monitor weather conditions carefully to ensure it was safe to launch.
Once they gave the go-ahead, the balloon would be partly inflated with helium and released from its launch vehicle.
"Because of the change in the atmosphere, the helium will expand until it's fully inflated and is about the same dimensions as the Dunedin stadium," Fairbrother said.
The pumpkin-shaped SPB is made from about 9ha of thin film resembling sandwich bags, reinforced with load-carrying tendons. Drifting at an altitude of about 33.5km carrying 2300kg of tracking and communication instruments, it was expected by Nasa to circumnavigate the globe once every one to three weeks.
It was hoped it would eventually come down in Argentina, although Nasa would have little control over the balloon once it was airborne.
"We can drop ballast or open a valve and let out helium, so from that perspective we can change our altitude slightly. But in general we're following the winds," Fairbrother said.
"Our target is [to stay airborne for] 100 days but if we get only 10 or 20 days I'd be ecstatic."
As the balloon travels around the Earth it may be visible from the ground, particularly at sunrise and sunset. Nasa launches up to 15 similar balloons annually. If the Wanaka launch goes well, Nasa will consider returning to the southern tourist town.
Track the balloon's progress here.
