In building design, wind loads are considered similar to earthquake loads in the calculation of lateral forces for resistance. Most people realize that a building is designed to withstand vertical gravitional forces. It is built to stand up. But, a building is also design like a cantilevered beam meant to resist lateral forces, such as wind and vibration. When a tower is designed, the maximum sustained wind taken from historic data assembled with charts provided in the applicable building code, is applied across the face of the building to calculate it overturning moment. The building is then designed structurally to resist that moment. The wind speeds accompanying Katrina could be in excess of the maximum known winds for the towers designed in New Orleans. The lateral forces presented by this storm could very well be in excess of the resisting moments of these buildings. Add to that the additional force of waves battering the lower floors and the danger is exponentially worse.
Understand this. In structural design for lateral loads in modern buildings, maximum wind loading is never, repeat never, considered in conjuntion with a seismic event. The odds are so great against the possibility that it is simple not required. Combine sustained winds in excess of the maximum design load, combined with lateral wave loads stiking the buildig in similar fashion to a seismic event, and there is a very real possibility of building collapse during this storm... ESPECIALLY highrises. Catastrophic building failure is a very real possiblity.