updated 12/21/2005 11:44:03 AM ET 2005-12-21T16:44:03

Researchers say Hurricane Katrina was a weaker storm than first thought when it slammed the Gulf Coast, with the strength of a Category 3 storm instead of a Category 4.

New data shows Katrina’s top winds were about 127 miles at impact, and that New Orleans and Lake Pontchartrain were likely spared the storm’s strongest winds, according to the National Hurricane Center.

New Orleans’ storm levees were believed to be able to protect the city from the flooding of a Category 3 storm. But portions of the levee system were either topped or failed, leaving up to 80 percent of the city under water.

An investigation into why the system failed is under way. Jim Taylor, a spokesman for the Army Corps of Engineers, said the storm’s category downgrade won’t affected any proposed changes under debate.

Louisiana Sen. Mary Landrieu, a Democrat, said: “This news further highlights the need for a full federal commitment to build the highest level of protection through levees and coastal restoration for New Orleans, South Louisiana and the Gulf Coast.”

Further study on the strength
Category 3 storms range from 111 mph to 130 mph, so Katrina was on the the strong side of that ranking. Category 4 storms run from 131 mph to 155 mph. Katrina was a top-scale Category 5 with 175-mph winds while in the Gulf of Mexico.

Forecasters revised the storm’s strength after studying data from devices that were dropped into Katrina from hurricane hunter aircraft, hurricane specialist Richard Knabb and forecasters Jamie Rhome and Daniel Brown said in the center’s final report.

The change also came from reviewing readings from a device called a stepped frequency microwave radiometer, which measures wind speed by examining how sea foam is blown. Radar images taken by hurricane hunter aircraft also were used.

Although an accurate reading of the highest winds in the New Orleans area were made difficult by the failure of measuring stations, a NASA facility in eastern New Orleans measured a sustained wind of only about 95 mph, the report said.

It was likely that most of the city experienced winds of Category 1 or 2 strength, a range from 74 mph to 110 mph, the report said, although winds on the upper floors of high-rise buildings could be up to a category higher.

Katrina killed more than 1,300 people in Louisiana, Mississippi, Florida, Georgia and Alabama. It is expected to cost insurers at least $34.4 billion in claims.

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