New Orleans - New Orleans on Tuesday marked 12 years since Hurricane Katrina slammed into the US Gulf Coast, as the low-lying coastal city braced for a potentially-devastating new impact by Harvey later this week.As the storm churned over warm Gulf waters, meteorologists predicted that Harvey would make landfall for a second time late Tuesday or early on Wednesday morning over Louisiana, the state directly to the east of Texas.Fifty mm of rain had already fallen by Tuesday morning in Louisiana's most vulnerable city New Orleans, which lies below sea level and relies to stay dry on a network of pumps, which have been plagued by a string of failures in recent weeks. Forecasters predicted flash flooding would follow in the city famous for its jazz music and cuisine, where Katrina caused widespread devastation in 2005, killing 1 800 people and causing $108 billion in damage. "Today, we are a resilient city with greater resolve, but we remain vigilant in the face of another threatening storm," New Orleans Mayor Mitch Landrieu said. Schools and public buildings were closed, and the mayor urged residents to remain home and off the streets. Many had already been filling sandbags for days. Officials expressed cautious optimism that water pumps would be able to handle the deluge, despite a series of mechanical failures in the last several weeks. "There are some forecasts for up to 250mm of rain over the next 36 hours or so for New Orleans. I would definitely not be surprised if it became more than that," meteorologist Eric Holthaus told AFP.The city held its collective breath, hoping to avoid the destruction brought on by Katrina, which flooded 80% of New Orleans leaving an indelible mark on the city.Still bearing Katrina's scars, Louisiana's so-called "Cajun Navy" - a caravan of trucks and boats - went to Houston over the weekend to help with rescues. "No city welcomed more New Orleanians following Katrina than Houston, and our hearts break for them as Hurricane Harvey displaces so many of their citizens," Landrieu said.The National Guard has positioned 400 airmen in Louisiana while New Orleans collected 40 boats and 20 high-water vehicles, in preparation for Harvey's onslaught.