NHC: The massive storm surge produced by Katrina, even though it had weakened from Category 5 intensity the previous day to Category 3 at landfall in Louisiana, can be generally explained by the huge size of the storm. Katrina had on 29 August a large (about 25-30 n mi) radius of maximum winds and a very wide swath of hurricane force winds that extended at least 75 n mi to the east from the center.
TampaSteve: Ivan in 2004 had hurricane force winds at landfall extending 105 n mi from the center. In addition, Ivan was a Category 5 for some 60 hours, and a Category 4 until right before landfall.
NHC: Even though Hurricane Camille (1969) was more intense than Katrina at landfall while following a similar track, Camille was far more compact and produced comparably high storm surge values along a much narrower swath.
TampaSteve: What about Ivan? You are comparing Katrina to the wrong hurricane!
NHC: Also, Katrina had already generated large northward-propagating swells, leading to substantial wave setup along the northern Gulf coast, when it was at Category 4 and 5 strength during the 24 hours or so before landfall. In fact, buoy 42040, operated by the National Data Buoy Center (NDBC) and located about 64 n mi south of Dauphin Island, Alabama, reported a significant wave height (defined as the average of the one-third highest waves) of 30 feet as early as 0000 UTC 29 August. This buoy later measured a peak significant wave height of 55 feet at 1100 UTC that matches the largest significant wave height ever measured by a NDBC buoy.
TampaSteve: Yes, it matched the record wave height recorded in Hurricane Ivan in that very same area.
NHC: Overall, Katrinas very high water levels are attributable to a large Category 3 hurricanes storm surge being enhanced by waves generated not long before by a Category 5 strength storm.
TampaSteve: Waves are not surge! But let's say for the sake of argument that waves are a major factor in surge height. Ivan's waves were at least as high as Katrina's, so the "wave setup" explanation doesn't cut it.
Again, if Katrina made landfall with maximum sustained winds and windfield size comparable to Hurricane Ivan, how did it carry a surge almost twice the height of Ivan's into the Gulf Coast???
The answer is simple: Katrina was a solid Category 4 at landfall, not a Category 3 as stated in your final report. Your final report is in error and should be revised.
