I agree that the first 24 hours after Katrina hit NO, the reports were quite optimistic that the city had been hit, but spared the most severe outcome of a levee break. It does seem to me that I remember later on Monday some mention of flooding beginning in NO, but the exact nature of the seriousness was not known until early Tuesday.
And throughout the entire time, both Nagin and Blanco seemed clueless.
My recollection on watching the news on Tuesday morning following the hurricane was that the Mississippi coast had been flattened, but New Orleans had again dodged a bullet. I didn't hear anything about flooding until later on Tuesday.
http://www.freerepublic.com/focus/f-news/1477255/posts
has a timeline.
check the original timeline for updates
http://rightwingnuthouse.com/archives/category/katrina-timeline/
Levee break was known late Monday AM, but not mentioned by the Mayor as a cause for alarm until late TUESDAY afternoon, well after looting began and it was known the water was still rising.
The mayor was playing chicken and he lost!