A storm forecasters warn is carrying “off the chart” amounts of moisture has made landfall on the US Gulf coast, having already caused widespread power cuts.
Tropical storm Barry, which had officially strengthened into a category one hurricane on Saturday morning with maximum sustained winds of 75mph, is causing downpours that could last for days in a test of flood-prevention efforts implemented after Hurricane Katrina devastated New Orleans 14 years ago.
Its rating as a hurricane was downgraded once more as it hit land but authorities are braced for the worst.
As residents and tourists in the Big Easy, Baton Rouge and other heavily populated areas in the storm’s path hunkered down, the Coast Guard rescued more than a dozen people from the flooded remote island of Isle de Jean Charles.
- ITV News Correspondent Emma Murphy says some residents have been ordered to evacuate
Water on the island, which is about 45 miles south of New Orleans, had risen so high that some residents were clinging to rooftops by the time help arrived.
Meanwhile, a levee in Plaquemines Parish, a finger of land extending deep into the Gulf of Mexico downstream from New Orleans, has already been topped by water.
And, residents in Terrebonne Parish, at the heart of the Cajun culture in southern Louisiana, were issued with a mandatory evacuation notice as Barry bore down.
- ITV News' Emma Murphy reports on how conditions are deteriorating rapidly
But officials remain confident New Orleans’ levees will hold firm, with most ranging in height from 20ft to 25ft.
Officials predict Barry will make landfall near Morgan City, west of New Orleans.
More than 70,000 customers are without power owing to outages caused by the storm, including 66,830 in Louisiana and 3,140 in Mississippi.
National Hurricane Centre director Ken Graham, giving an update via Facebook Live, pointed to a computer screen showing a huge, swirling mess of airborne water.
He said: “That is just an amazing amount of moisture. That is off the chart.”
Barry is moving so slowly that it is likely heavy rain will continue throughout the weekend across Louisiana, he added.
There are predictions of 10-20in through Sunday across a swath of Louisiana that includes New Orleans and Baton Rouge, with some parts of the state possible getting 25in.
Looking ahead, tracking forecasts show the storm moving towards Chicago, swelling the Mississippi River basin with water that must eventually flow south again.
Governors have declared emergencies in Louisiana and Mississippi, and authorities have taken unprecedented precautions in closing floodgates and raising the barriers around New Orleans.
Governor John Bel Edwards said it is the first time all floodgates have been sealed in the New Orleans-area Hurricane Risk Reduction System since Katrina.
But he still said he does not expect the Mississippi River to spill over the levees despite water levels already running high from spring rains and melting snow upstream.
Rescue crews and about 3,000 National Guard troops are posted around Louisiana with boats, high-water vehicles and helicopters.
President Donald Trump has declared a federal emergency for Louisiana, authorising federal agencies to co-ordinate relief efforts.