Ex TC Ellie could move out to sea and reform,The bureau's Greg Connor told ABC Radio.
He said that the low would bring even more rain.
Major flooding was expected on the Herbert River on Monday night, and smaller rivers were already experiencing moderate flooding, Mr Connor said.
"We're certainly not out of the woods regarding this low," he said.
"There's a couple of scenarios we're looking at.
"One is that it moves further inland, which would still produce quite a bit of rain for the Townsville area, the other is that it, by Wednesday, starts moving out over the coast, and re-forms as a cyclone.
The last TC track map I saw this morning showed the low hooking to the south and then back out to see. The image is no longer available.