Hurricane Katrina was the third-most intense hurricane to ever hit the United States since reliable records began in 1851, according to the National Weather Service. Only the "Labor Day Hurricane" that hit the Florida Keys in September 1935 and 1969's Hurricane Camille were more intense.
As measured by barometric pressure, Katrina was more intense than Hurricane Andrew, which roared across south Florida in August 1992. Barometric pressure is the most accurate representation of a storm's power. The lower the barometric pressure, the more intense the storm.
Katrina's winds at landfall were 140 mph, which places the storm as a strong Category 4 on the Saffir-Simpson scale of hurricane intensity. Andrew was a Category 5 storm, with winds of 165 mph when it made landfall south of Miami.
Wind speed is the primary factor for determining the categories of hurricanes, superceding barometric pressure.
Both Katrina's wind speed and barometric pressure were measured by a U.S. Air Force reconnaissance aircraft at 6:00 a.m. CT Monday morning, just prior to landfall in southeastern Louisiana.
National Weather Service spokesman Chris Vaccaro said today that official NWS land-based measurements of Katrina's wind speed and barometric pressure at landfall might exist, but the data that's stored in instruments isn't available due to loss of power. The data can only be retrieved once power is restored.
Of the three most intense hurricanes ever to hit the USA, two — Camille and Katrina — made landfall within less than 50 miles of each other along the Gulf Coast.