The perception of a hurricane's structure at landfall may have dramatic consequences in actions taken before and during the storm, and also afterward. Many coastal Mississippi residents who experienced Hurricane Katrina thought that the storm would be similar to several others which had made landfall in that hurricane-prone area over the last several decades; however, their misconception of Katrina's structure often greatly (and sometimes fatally) surprised those residents when the storm actually turned out to be much different. Well after the storm, the continued perception of Katrina's “typical hurricane structure” has led to very contentious insurance-related issues along the northern Gulf Coast. Katrina was experiencing an eyewall replacement cycle upon landfall; therefore the storm likely struck the northern Gulf Coast with not one eyewall, but two. The growth of this outer eyewall had a significant influence on the great expansion of the radius of hurricane-force winds in the hours prior to landfall and resulted in both the early arrival and far-reaching influence of severe eyewall-like winds along the coast.

Through the University of South Alabama's Coastal Weather Research Center, I provided tailored hurricane forecast information to approximately 100 industrial clients along the southeast Atlantic and Gulf Coasts during Katrina; several of these clients were in the path of Katrina and I was in direct communication with some of them on the Mississippi Coast prior to and during the actual landfall event. The early arrival of Katina's outer eyewall was a great surprise to many in the storm's path. One client in Gulfport on the Mississippi Coast had relocated their emergency operations center several miles inland to near I-10; they personally related their shock on the phone when exceptionally strong easterly winds at their location were already blowing numerous windows out of cars and downing large trees hours before Katrina's eye arrived on the Mississippi coast. Their vehicles were sheltered from southerly winds, but not winds from the east. Having already lost their internet connection very early in the storm, the frustrated client was commenting on how bad things were outside and asking me if the storm had suddenly accelerated and the eye was now making landfall? My somber response was that the eye was still well offshore and that even stronger winds from the south would arrive later as the center made landfall to their west. Hours later, the client later relayed their horror when the winds indeed shifted to south and water flooded their control room and washed all their cars away in an area which had always been a safe haven in earlier storms, including Camille.

Other survivors waited to evacuate until early Monday morning, to see whether they would experience the eyewall, not realizing that Katrina had two of them. Thinking they would not experience the worst of the storm, people well east of the storm's projected path were greatly surprised when conditions became severe. After a suspense-filled night, some were actually caught outside doing last-minuted inspections of their homes and property after sunrise when exceptionally strong easterly winds arrived hours before the eye made landfall; falling trees and flying debris prevented their escape to areas farther inland. Hours later their homes experienced a devastating storm surge.

There is ample meteorological evidence to show that Katrina likely contained two eyewalls at landfall. My post-storm assessment of Katrina's structure at landfall on the Mississippi/Louisiana coast varies from the assessment of some others and this apparently has led to very contentious insurance-related issues in that region.

I will present my personal experience of both talking with clients on the Mississippi coast before and during the event, and my own reconstruction of Katrina's landfall structure based on a combination of 1) data from numerous meteorological platforms and 2) eyewitness survivor accounts which strongly suggest that Katrina had two eyewalls at landfall. Finally, I will summarize how perceptions of a single vs. a double eyewall storm at landfall has dramatically impacted issues related to 1) why people stayed on the Mississippi Coast during the storm, and 2) some of the home-owner insurance litigation in the post-Katrina recovery period.