Hurricane Katrina weaker than thought at landfall

Hurricane Katrina was weaker than previously thought when it came ashore near New Orleans on August 29 and smashed the levees protecting the city from floodwaters, US forecasters said.

The US National Hurricane Centre's revised estimate of Katrina's intensity could be important because the levee system was supposed to withstand the weaker storm that turned into the costliest natural disaster in US history and one of the deadliest with more than 1,200 victims.

The centre said a review of weather data suggests Katrina came ashore near the Louisiana coastal community of Buras at the high end of Category 3 intensity with maximum sustained winds of just under 130 mph (209 kph).

It had originally said Katrina made landfall as a Category 4 storm, with 140-mph (225-kph) winds before weakening to a Category 3 hurricane with 125 mph (201 kph) winds when it made a second landfall on the Mississippi coast later in the morning.

Hurricanes are rated according to the five-step Saffir-Simpson scale, with Category 5 storms boasting winds in excess of 155 mph (249 kph) ranked as the most powerful.

The levee system, which Katrina breached in 50 places, was designed by the US Army Corps of Engineers to protect New Orleans from a Category 3 storm, with sustained winds of up to 130 mph (209 kph).

The centre noted that due to Katrina's immense size, Category 4 strength winds might have been felt on the Louisiana coast near New Orleans while the eyewall of the storm was still a couple of hours away from official landfall.

The hurricane center's report, posted on its website on Tuesday, also said it appeared that Katrina's storm surge reached 27 feet (8.2 metres), a foot (0.3 metre) less than previously reported.

The wall of water swept at least 6 miles (9.7 km) inland in many places and up to 12 miles (19 km) inland along bays and rivers.

It was the surge, rather than the storm's winds, that strained the levees in the New Orleans area, the centre said.

"The massive storm surge produced by Katrina, even though it had weakened from Category 5 intensity the previous day to Category 3 at landfall in Louisiana, can be generally explained by the huge size of the storm," it said.

Katrina's most destructive core was up to 30 nautical miles (55.6 km) in radius, while hurricane-force winds extended at least 139 km to the east of the centre.

The storm surge was enhanced by the large waves that Katrina whipped up in the Gulf of Mexico while it was an extremely powerful Category 5 storm. The centre said one buoy measured a wave 55 feet (17 metres) high.

The centre said Katrina's direct death toll was estimated at about 1,200, of which some 1,000 were in Louisiana and 200 in Mississippi. That toll would make Katrina the third or fourth deadliest hurricane in US history.

A higher figure of 1,336 given by officials included people whose deaths were indirectly related to the storm.

As for damages, the hurricane centre said a preliminary estimate put them at around $75 billion.

"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 (in 1992)," it said.

- REUTERS