"It was apparent [on Friday and Saturday] that when [Katrina] got back into the Gulf, it was going to intensify," Landsea said. "Saturday the conditions looked perfectwarm deep water, no wind shear, and moist air."
On August 27 Hurricane Katrina was a spectacular sight from above. The storm's clouds covered the entire Gulf of Mexico, Landsea said.
By 11 a.m. August 28 Katrina had become a Category Five storm, the most powerful type of hurricane. Its strongest winds were blowing at 175 miles an hour (280 kilometers an hour).
At 5 p.m. the National Hurricane Center issued an advisory describing Hurricane Katrina as a "potentially catastrophic" storm. The storm had started to push a wall of water from the Gulf of Mexico towards land, and the advisory warned of storm surge flooding of 18 to 22 feet (5 to 7 meters).
"It was clear that there was going to be a horrible storm surge across a large region," Landsea said.
Landsea made his last flight into Hurricane Katrina just as the storm was about to slam into the Gulf Coast. The storm's strength had diminished. But Katrina's winds were about 140 miles an hour (225 kilometers an hour) when the hurricane made landfall in Louisiana near the mouth of the Mississippi River.
"One thing that was nice to see was that it was starting to weaken," Landsea said. "It was no longer a Category Five.
"We're not really sure why it started to weaken," he added. "It may have had dry air coming off the continent that weakened it. There may have been wind shear."
Katrina also might have been undergoing an eye wall replacement cycle as it approached landfall, Landsea said. This phenomenon occurs periodically in extremely powerful hurricanes.
The eye wall is the term for the intense thunderstorms that whirl around the center of the hurricane. When a new eye wall starts forming around the existing wall, the event temporarily slows a hurricane's momentum. The storm's winds are weaker for a few hours until the replacement is completed.
"It looked a lot like [Katrina] was trying to go through one of these cycles," Landsea said. "Its eye was fairly lopsided at landfall with most of the rainfall on the north side of the eye wall. The south eye wall was falling apart."
But Katrina's storm surge diminished little, if any, as it came ashore.
"It was a larger system, and the storm surge was spread out over a larger area," Landsea said. "Even though Katrina was starting to weaken before it made landfall, because it was a large system, the ocean takes a while to relax."
Landsea and others aboard that last flight into Katrina initially thought the Gulf Coast had been spared at least some of the hurricane's wrath.
"We were upbeat at the end of the flight," Landsea said. "It wasn't until later that we found out how horrible it had been."
Hurricane Katrina's storm surge broke through the levees protecting New Orleans, flooding about 80 percent of the city. In Mississippi the beachfront cities of Biloxi and Gulfport sustained massive damage.
The death toll is still being tabulated, but it is already more than 700. Damage from Katrina is expected to exceed 200 to 300 billion dollars (U.S.), making it the most expensive hurricane in U.S. history.
Willie Drye is the author of Storm of the Century: The Labor Day Hurricane of 1935, published by National Geographic.
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