I believe it's been estimated that Katrina will increase the annual federal budget deficit by $100 billion. I'm not sure if this is purely from expected outlays, or if it takes account of macro effects on existing programs (e.g., reduced income and payroll tax revenues from the hit to economic activity, more unemployment insurance payouts, etc.).
This of course is on top of what were already projected to be huge deficits. And it helps to show why budgetary targets and planning ought to take account of the possibility that there will be adverse shocks from time to time.
A further problem is that the Administration had been claiming it would cut the 2004 deficit in half by the end of Bush's second term. Most experts expected this target not to be met, other than through gamesmanship redefining the target so that it could ostensibly be met (a la monthly military recruiting targets). In addition, even if the target was met, the deficit was projected to explode again as soon as Bush was safely out of office.
Katrina not only means that the deficit reduction target can't be met, but also that there is now an excuse for not meeting it. If the Administration's behavior in 2001 is any guide, this suggests that they will regard the deficit reduction pledge as having been completely called off. So perhaps any deficit at all is now politically permissible, since the excuse "We would have done what we promised, except for Katrina" can be used even if Katrina is responsible for only a small percentage of the shortfall.
Since I have to get back to writing my fiscal language book, perhaps this is enough cheerful thoughts for one day.