Actually, it does just the opposite of what you are thinking, but this will take some explaining. It supports free will, but you will have to think hard about this and I have had a hard time explaining in the past to those with the Open View and those with a strong God controls all the future view.
First you have to look at and study the options:
Option one: The future is unknown to God, except for what He will do: How would God state a “warning” to a nation that is bad at the time of the warning? God would say: “If you do not repent I will destroy you.” God would not say: “I will destroy you”, because He might not destroy them, so He would lie if He said He would. The “if” would say: God does not know the future.
Option two: God knows all the future perfectly (it is in stone), including all free will choices: How could God give a warning to a nation that is doing badly and needs to change and God knows a warning is what they need to change and will change with a warning. If God said: “if you do not change I will destroy you.” God is misleading, since the “if” says He does not know the future result. If God said the truth: “I will not be destroying you because you will repent”, there would be no warning, so they would not repent (God is no help).
Option three: God knows the future perfectly, but through His prophets conveys the truism which Jerimiah finally records for us, that God can factually state actions He will do for or against a nation in the future against or for a nation or individual which can later not happen if the nation or individual He stated the action to is no longer the same when the action is to take place. This would need to be stated generally with no specific nation, person, time or action being addressed. God will not be using the word “if” when addressing future actions for or against a nation or individual, so it is up to their knowledge of how God states warnings to understand His warnings.
Look at Jonah, since here we have a “warning” stated as only a single future action of God in a specific time frame: “I will destroy you in 40 days.” Jonah definitely understood that as a warning for Nineveh and from the reaction of the people of Nineveh they understood it as a warning. We can understand Jonah knowing it was a warning, but how did Nineveh know? First off: the story is all about Jonah and this is really being done to help Jonah, with Nineveh being the back drop to the story. God could have found other prophets to go to Nineveh, but Jonah needed help. We do not know all the other previous prophets who went to Nineveh and what they said about Jonah’s coming or what the people will need to do to avoid God’s wrath nor what the people were taught about warnings from God. Jonah could not have told the people repent or God will destroy you in 40 days, since that would suggest God did not know what He would be doing in 40 days.
How did I do?