This article is more than 1 year old

This article is more than 1 year old

A potential tropical storm brewing in the Gulf of Mexico presents twin troubles for parts of south-east Louisiana: the possibility that a high Mississippi River will be lapping at the tops of levees this weekend and a danger of flash floods like the one that hit New Orleans on Wednesday.

The Gulf of Mexico disturbance that dumped as much as 20cm (8in) of rain in parts of New Orleans in three hours was forecast to strengthen into a tropical depression on Thursday, a tropical storm called Barry on Thursday night and possibly a weak hurricane by Friday.

Forecasters said Louisiana could receive up to 30cm of rain by Monday, with isolated areas receiving as much as 46cm. The storm’s surge at the mouth of the Mississippi could also mean a river that has been running high for months will rise even higher.

Mississippi and Texas were also at risk of torrential rain.

New Orleans got an early taste on Wednesday of what may be in store. News outlets said a tornado may have been responsible for wind damage to one home, while some city-centre hotels and businesses were flooded as streets became small rivers that accommodated kayakers. The floods paralysed rush-hour traffic and stalled cars around the city.

And it all happened fast.

“I must have got to work about a quarter to seven,” said Donald Smith, whose restaurant flooded for the third time this year. “By 7.15, water was everywhere.”

It brought memories of a 2017 flash flood that exposed major problems – and led to significant personnel changes – at New Orleans’ sewerage and water board, which oversees street drainage. City officials said the pumping system that drains streets was at full capacity. But the immense amount of rain in three hours would overwhelm any system, said the board director, Ghassan Korban.

Threats of a high Mississippi prompted officials in Plaquemines parish at Louisiana’s south-eastern tip to order evacuations of some areas to begin on Thursday. A voluntary evacuation was called on Grand Isle, the vulnerable barrier island community south of New Orleans. The state governor, John Bel Edwards, declared a statewide emergency.

A spokesman for the US Army Corps of Engineers in New Orleans said the agency was not expecting widespread overtopping of the levees but there were concerns for areas south of the city. The weather service expects the river to rise to 6 metres (20ft) by Saturday morning at a key gauge in the New Orleans area, which is protected by levees 6 to 7.6 meters high.

The corps was working with local officials downriver to identify and reinforce any low-lying areas, he said. He cautioned that the situation may change as more information arrives. “We’re confident the levees themselves are in good shape. The big focus is height,” he said.

Edwards said National Guard troops and high-water vehicles would be positioned all over the state. “The entire coast of Louisiana is at play in this storm,” the governor added.

New Orleans officials have asked residents to keep at least three days of supplies on hand and to keep their neighbourhood storm drains clear.

As the water from Wednesday morning’s storms receded, people worried about what may come next.

Tanya Gulliver-Garcia was trying to make her way home during the deluge. Flooded streets turned a 15-minute drive into an ordeal lasting more than two hours.

“This is going to be a slow storm … That’s what I’m concerned about,” she said.

Floyd and Missy Martin, two tourists from Raleigh, North Carolina, were trying to make the best of it at a store with puddles on the floor where they were buying an umbrella, two bottles of merlot, chips and peanuts.

“We could drown out our sorrows or make an adventure of it,” Floyd Martin said, joking.