Hurricanes are notoriously difficult to forecast. When I started at WVEC, WAY back in 1995, the National Hurricane Center would only issue a three day forecast for tropical systems. Now, we are up to a five-day forecast. While this may help in planning, as we are seeing in New Orleans right now, it can also lead to greater uncertainty in the forecast track. To "fix" that, the National Hurricane center issues a forecast which has a cone shaped, indicating where the storm may go.

As we can see from the Hurricane Center forecast, there is a center-line track with the "most likely" path of Gustav - but there is also a white cone, showing Gustav's possible path.  This means, as of Saturday afternoon, places to the west of New Orleans, like Houston, are not "out of the woods."  It's entirely possible Gustav could go west and hit the Texas coastline - and the "cone" shows the uncertainty in Gustav's path.  So don't pay attention to JUST the center line, but the entire cone path.