storm surge is like a bubble created on the ocean surface where it wells up due to dramatically lower air pressures near the center of the storm. air pressure is a large determining factor in surge, and katrina typically had a lower pressure than the winds supported. the pressure was around 920mb, which is a borderline 5, when it crossed the miss delta. when it reached the pearl river area, it was up to 930mb, still a solid category 4. forward speed of the hurricane also contributed to the surge height, as well as the large wind field, which contributed to the huge extent of coastline that was flooded. these factors working together created a surge uncommon in its height and extent along the coastline.
i honestly thought storm surge was done as the major killer in hurricanes. the last time an event like this, where a large number of people drowned by surge, was in 1969... camille. people were told that the ocean was coming up to get them. i don't know why someone would stay, with that prospect.
HF 1650z31august