If you read carefully the Old Testament, in many instances where Yahweh is said to predict something to happen in the future, it is stated or implied that he makes that thing happen. It is even one possible meaning of the name Yahweh.
This way also you and me can predict the future: If there is a banana on a table, predict that it will soon be on the floor, then drop it down and there it is!
For this kind of predictions one does not need to determine the inital state of things or consider possible scenarios or to do complicated calculations. In fact such an analysis in many cases would be impossible, even for a god.