In this excellent little section on God's anger (reprinted below from CCEL), Augustine notes that God's anger is not the Lord losing control, but rather is His response to and punishment of sin. This is never disconnected from reason (even when focused on irrational animals), but rather is designed both to teach us about God and about what sin deserves and, presumably, give us a chance to repent when we hear that it's coming.
The anger of God is not a disturbing emotion of His mind, but a judgment by which punishment is inflicted upon sin. His thought and reconsideration also are the unchangeable reason which changes things; for He does not, like man, repent of anything He has done, because in all matters His decision is as inflexible as His prescience is certain. But if Scripture were not to use such expressions as the above, it would not familiarly insinuate itself into the minds of all classes of men, whom it seeks access to for their good, that it may alarm the proud, arouse the careless, exercise the inquisitive, and satisfy the intelligent; and this it could not do, did it not first stoop, and in a manner descend, to them where they lie. But its denouncing death on all the animals of earth and air is a declaration of the vastness of the disaster that was approaching: not that it threatens destruction to the irrational animals as if they too had incurred it by sin.Chapter 26:
So when the anger of God was poured out on the world in a flood, God likewise provided us with a picture of His mercy in Noah and the ark, which is a picture of Christ and the church.
We must understand the story of the flood both as literally true and as being a picture of something higher than itself--namely of the destruction of the city of man and the salvation of the City of God.