Wikipedia has an entry up for Hurricane Katrina, the category 5 hurricane that’s predicted to have a good chance of hitting the city of New Orleans, Louisiana.
As the Wikipedia entry on New Orleans suggests, the world-famous town is especially vulnerable to storms as the entire city is located below sea level in a land area that acts like a large bowl, trapping water inside the city.
The city is protected by large rings of levees that keep the surrounding water at bay, while pumps remove any water brought in by storms. However, predictions of storm surges 26 feet higher than normal tides have resulted in a mandatory evacuation order to be issued.