Storm Barry has made landfall in Louisiana, where officials have warned of potentially life-threatening floods.
The storm reached hurricane-strength as it neared the coast, but has now weakened to a storm packing sustained wind speeds of 112km/h.
The system is crawling north-west at a speed of just 9.6km/h, dumping heavy rainfall as it tracks inland.
The worst of the storm is expected to hit an area west of New Orleans, and affect the wider region.
Thousands have been evacuated from areas most at risk of flooding and other residents have been told to shelter in place.
About 100,000 households are already without power.
All flights in and out of Louis Armstrong New Orleans International Airport have been cancelled.
President Donald Trump declared a federal state of emergency in Louisiana before the storm hit.
What is the latest?
In its latest update, the US National Hurricane Centre (NHC) confirmed Storm Barry's winds had slightly weakened.
Before it made landfall near Intracoastal City, it was confirmed as the first hurricane of the 2019 Atlantic season.
As the storm's rain bands closed in, local journalists shared images of flooding in some residential areas.
Flooding on Jean Lafitte Blvd. (LA45) pic.twitter.com/W5uaKxQWNe— Paul Dudley (@Pauldudleynews) July 13, 2019
At least one levee, in Plaquemines Parish in the state's tip, was already overtopped by water by midday on Saturday.
Officials have told residents there to immediately evacuate, if it safe to do so, or risk being cut off for several days.
Louisiana's most populous city, New Orleans, looks set to avoid a direct hit from the hurricane - with the worst expected further west near the city of Lafayette instead.
Heavy rain is expected throughout the state, with warnings that of up to 66cm of rain could fall in places.
Louisiana's governor, John Bel Edwards, has urged residents not to become complacent.
"I want to caution everybody. This is just the beginning," he said at a news conference.
With recent flash-flooding and heavy rainfall, there was particular concern about the flooding risk to low-lying New Orleans.
Most of the city's flood defences, improved after more than 1800 died in Hurricane Katrina in 2005, are built between 6-7.6 metres high.
The National Weather Service earlier warned the Mississippi River could crest at 6m during the storm, but yesterday revised their estimate down to 5.1m.
No city-wide mandatory evacuation is in place, but locals were told to hunker down and stock-up on essentials.
The city's emergency preparedness campaign has urged residents to remain vigilant and stay patient.
Hurricane Barry is expected to gradually weaken as it moves inland across the weekend.