It was the storm that laid waste to an area along the US Gulf Coast about the size of England, in the process wreaking havoc on one of America's legendary cities. It also changed the perception of a presidency, perhaps forever.
Today George Bush returns to New Orleans, exactly a year after Hurricane Katrina, on his 13th visit since the storm, for an anniversary that has been designated a national day of remembrance. Katrina was not only the most expensive national disaster in US history, leaving an insurance bill for the devastation in Louisiana, Mississippi and Alabama of some $60bn £32bn). The total cost human and emotional as well as economic has been far higher still.
Some 1,600 deaths are now attributed to the storm. Some Gulf Coast communities were virtually wiped off the map. In New Orleans itself, half of the 500,000 inhabitants pre-Katrina have yet to return and many of them surely never will. Ray Nagin, the mayor, says population recovery will take five years, but that may be optimistic.
In some parts of New Orleans life has returned. The French Quarter is again aglitter with neon and sanitised sin, with signs proclaiming " Happy Hour, All Day, All Night."
A year ago, the Superdome, packed with refugees in scenes of Third World squalor, was a symbol of how the richest country on earth had failed its neediest citizens. Yesterday a last crew of workers was finishing the repainting of the roof, ready for the return of the city's NFL team. " Go Saints," a giant poster proclaimed, "Re-opening September 25."
But elsewhere the recent apocalypse is all too visible. The lower Ninth Ward, a poor black neighbourhood, is effectively abandoned, a frozen shapshot of the day the floods receded. But even in the once-prosperous white district a couple of miles north-west of the centre, almost all is desolation.
A few of the houses that last September were 10 feet under water are being restored, and a few have been pulled down - "We Tear Down Houses" reads an advertisement nailed to one empty home, three-quarters obscured by rampant foliage that has turned a trim suburban garden into a jungle. Everywhere there are piles of litter, and an atmosphere of sadness and palpable worry.
"We're still not prepared," said one New Orleanian. "A year on, and the same thing could happen again. Everyone blames everyone and so little gets done."
The bulk of those who have left the city are black and poor, with little financial stake in what, long before Katrina, was one of the worst-run cities in the country. In their absence, New Orleans' character, both ethnic and political, cannot but change.
A year after the hurricane and the storm surge which breached the city's levees and left 80 per cent of it under water a third of the debris has yet to be removed. Vast tracts of the all-but-obliterated Ninth Ward look as they did when the floods finally receded last October. They have not been rebuilt and probably never will be.
The same may go for the standing of the President, as he vows today again to see through the rebuilding of the city, promising to his country that " never again" will it be unprepared for such a catastrophe. Nothing even Mr Bush's talented speech-writers come up with will make good the damage done. "Compassionate conservativism" was the slogan on which he was elected six years ago. But the image of him surveying the disaster from aloft amid the comfort of Air Force One as it made a detour from California to Washington definitively banished any such notions.
In those dreadful days after the storm, the authorities seemed not to grasp the scale of the disaster. Mr Bush's approval rating tumbled to below 40 per cent, where it has remained. The mess in Iraq, of course, had heavily contributed to his troubles. But Katrina delivered a coup de grace.
Since then things have improved but slowly. Congress has allocated $110bn for reconstruction. But precisely how much has been spent is debatable. Housing plans have been developed, and Congress has passed an act setting up a Gulf Opportunity Zone. But the focus has been on privately owned property, not the public housing where New Orleans' poorest used to live. The levees have been repaired but not to withstand the maximum Category Five hurricane that Katrina briefly was before it made land early on 29 August 2005. In other words, the flooding of New Orleans, for decades top of every expert's list of likely natural disasters in the US, could happen again.
For all this, Mr Bush, fairly or unfairly, is blamed. According to one poll this month, only 37 per cent of Americans approve of his handling of Katrina, compared with 42 per cent immediately after the storm. The consequences may become apparent in November's mid-term elections, at which the Republicans' control of both Senate and House of Representatives is at risk.
Senior Democrats have been swarming over New Orleans in the run-up to the anniversary, with a single message. The crisis had proved that their opponents were not fit to run the country.
Nature, however, deals in reality, not the statistics of political point-scoring. As New Orleans remembered Katrina, another hurricane called Ernesto was bearing down on Florida.
In this case, however, another Bush will be in charge: Governor Jeb of Florida, whose competence in matters of hurricanes even Democrats acknowledge.Reuse content