I think when we look at the tragedy of New Orleans, Dr. Mohler's response to this is one of theological balance. One quote in his commentary: Bad Theology Watch -- Who Speaks on od's Behalf? is the following dose of reality:
"God's wrath is even now being demonstrated in the events of human history, but not fully."
Within this tragety that has hurt so many, we need to give hope and see also that there is still mercy and grace of God in this. God wrath has yet to be fully revealed. The only way to avoid the full wrath of God is to repent and believe in Christ as the only satisfaction for the wrath of God against us.
Now where one goes an makes a hertodox statment in the time of crisis (and many know of misstatements in their lives which they regret), there will always be those that go off the deep end in trying to protect God from his sovereign control. We need look no further than Tony Campolo to Deny God's Omnipotence in his article: Katrina: Not God's Wrath--or His Will. This article is so unbiblical that I cannot say what god Tony Campolo actually worships.
Is Huricane Katrina an act of God's mercy or God's judgment? The balanced Answer is: Yes, it's both.
It will be more spiritually healthy to read some biblically balanced articles as:
The Goodness of God and the Reality of Evil by Albert Mohler
Hurricane Katrina by Philip Ryken
Point, Counterpoint by Philip Ryken