The US National Hurricane Center said that the storm was only a category three on the five level Saffir Simpson scale when it hit the US Gulf Coast on August 29.

It had previously been estimated at category four but the center said in its "Tropical Cyclone Report Hurricane Katrina" that the storm had weakened as it hit the coast.

The winds and storm surge breached water defences and floods devastated the city and killed hundreds of New Orleans residents.

The hurricane center's report said that the winds over the New Orleans region were probably less than category three when Katrina hit the city. The previous day Katrina had been category five.

The earlier estimate had Katrina's winds at about 240 kilometersmiles) per hour when it hit the coast. The new report said the winds were about 194km (120 miles) per hour.

The death toll from the storm currently stands at 1,336 with 1,090 in New Orleans and the rest of Louisiana, 228 in Mississippi, 14 in Florida and two each in Georgia and Alabama.

"Especially for Louisiana and Mississippi, the number of direct fatalities is highly uncertain and the true number might not ever be known," said the report.

The report said that the total damage cost of Katrina was assumed to be roughly twice the insured losses, about 75 billion dollars.

"This figure would make Katrina far and away the costliest hurricane in United States' history. Even after adjusting for inflation, the estimated total damage cost of Katrina is roughly double that of Hurricane Andrew (1992)," the center said.

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