Katrina only a Cat 1 in New Orleans?

Eye of Hurricane Katrina at sunset on August 28, 2005, when Katrina was at peak intensity. Photo credit: Deanna Hence. The photo was taken on NOAA hurricane hunter aircraft N43RF, which was participating in the Hurricane Rainband and Intensity Change Experiment, RAINEX, aimed to study the interaction between a hurricane's eyewall and the rainbands located outside the eyewall region, and how these changes affect hurricane intensity.

Was Katrina much weaker at landfall than originally thought? That's what analysis of the Katrina's wind data by Dr. Mark Powell of NOAA's Hurricane Research Division is showing. Dr. Powell is the world's expert on windspeeds measured in landfalling hurricanes, so his findings are being carefully studied by the National Hurricane Center (NHC) as they prepare their final report on Katrina. The NHC advisories had Katrina as a Category 4 hurricane with sustained winds of 145 mph when it struck the Louisiana coast near Buras, and a Category 3 hurricane with 125 winds when it passed 35 miles east of New Orleans. But Dr. Powell's analysis suggests that Katrina was a Category 3 hurricane with 115 mph winds at first landfall, and that the strongest winds that affected New Orleans were 95 mph. The analysis was done using data sources that were unavailable to the NHC in real time, including surface anemometers as well as Doppler radar measurements of wind speed from NOAA's hurricane hunter aircraft. While the results are still considered preliminary, I believe that when the official National Hurricane Center report on Katrina comes out in early 2006, Katrina will be "demoted" to a Category 3 hurricane. The full story was printed by the Florida Sun-Sentinel.

Many of the new ground based wind measurements were published on the New Orleans National Weather Service web site on Friday, October 7, in their post-storm report on Katrina. The highest sustained winds measured at any ground-based site were 90 mph on Lake Pontchartrain. The highest gust measured on the ground was 135 mph in Poplarville, MS. Many wind measurement sites failed during the storm, so we will have to rely on aircraft and Doppler radar to arrive at the true wind speeds of Katrina at landfall. Here's a few highlights of the highest winds measured at the ground during Katrina, before instrument failure:

New Orleans Lakefront Airport: sustained winds of 69 mph, gusting to 86 mph.
Biloxi's Keesler Air Force Base: sustained winds of 54 mph, gusting to 90 mph.
Gulfport airport: 46 mph, gusting to 58 mph.
Lake Ponchartrain mid-lake buoy: 90 mph, gusting to 114 mph.

Many of us heard that Category 5 winds were measured by the National Weather Service in Katrina. These rumors were aired as fact by television stations and other media outlets during the storm. However, as the post-storm report above outlines, these were just rumors, and no such winds were measured. If you listened to NPR last night, you also might have heard the story of how television stations in Baton Rouge were reporting a huge crime wave in Baton Rouge after the hurricane, and that an armed gang had even taken over the Mayor's office. These reports, later found out to be completely untrue, led to four-hour waits to buy guns at local gun stores in Baton Rouge. According to NPR, there was no increase in crime in Baton Rouge after the hurricane. The media, at times, did a poor job in separting fact from fiction during the storm, and there were in reality no sustatined winds above Category 1 measured on the ground during Katrina.

Obviously, a demotion of Katrina to Category 3 status would have political consequences. The levees of New Orleans were supposed to be able to withstand a Category 4 hurricane, and it appears as if they were done in by winds of only 95 mph--what one would find in a strong Category 1 hurricane. Still, Katrina at landfall in Mississippi was no ordinary hurricane. It brought the largest storm surge ever recorded in an Atlantic Hurricane to shore in Mississippi--28 feet, measured at the Hancock County, Mississippi EOC in Bay St. Louis. This is over five feet higher than the previous record set in Category 5 Hurricane Camille of 1969. So while the winds at landfall in Mississippi may have been Category 3 or even lower, the storm surge was a Category 5 plus! The storm surge levels that breached the New Orleans levees were probably characteristic of at least a Category 3 hurricane, and perhaps a Category 4. As both myself and Steve Gregory have emphasized in our blogs, the Saffir-Simpson scale of ranking hurricanes is inadequate; an additional scale ranking storms by damage potential from winds, storm surge and rainfall is needed. The reason no such scale has been implemented yet is that the NHC fears the added complexity may serve only to confuse the public. This is a valid concern, considering 40% of New Orleans' population before Katrina was illiterate, making hurricane education a very difficult undertaking in this city. Add to this the fact that many areas of the booming U.S. coast are being populated by hurricane neophytes, who just moved to the coast from areas that don't have hurricanes. Perhaps now that Katrina has gotten our attention, though, hurricane education will be an easier task, and we can start the talk about implementing a new damage scale.

Jeff Masters