Tropical Storm Cristobal has continued to weaken after it crashed ashore in Louisiana and created dangerous weather further east, sending waves crashing over Mississippi beaches, swamping parts of an Alabama island town and spawning a tornado in Florida.

Cristobal made landfall between the mouth of the Mississippi River and the since-evacuated barrier island resort community of Grand Isle, with 50mph winds.

Making landfall well under hurricane-strength, the storm had begun weakening as it moved inland — but heavy rainfall and a storm surge were continuing along the Gulf Coast, posing a threat across a wide area into the Florida Panhandle.

Cristobal’s forecast path takes it inland through southeast Louisiana, continuing north into Arkansas and Missouri by Tuesday, moving over Wisconsin on Tuesday night and into Canada by Wednesday, according to the latest advisory.

A wave crashes as a man stands on a jetty
A wave crashes as a man stands on a jetty near Orleans Harbour in Lake Pontchartrain in New Orleans (Gerald Herbert/AP)

In New Orleans, the question was how much rain would fall and whether there would be enough breaks in the bands of heavy weather for the beleaguered pumping system to meet its latest test of keeping streets free of floodwaters.

Coastal Mississippi news outlets reported stalled cars and trucks as floodwaters inundated beaches and crashed over roads. On the City of Biloxi Facebook page, officials said emergency workers helped dozens of motorists through floodwaters.

In Alabama, the bridge linking the mainland to Dauphin Island was closed much of Sunday. Police and state transportation department vehicles led convoys of motorists to and from the island when breaks in the weather permitted.

Forecasters said up to 12 inches of rain could fall in some areas, with storm surges up to five feet. The weather service warned that the rain would contribute to rivers flooding on the central Gulf Coast and up into the Mississippi Valley.

Storm surge covers a road
Storm surge covers a road in Long Beach, Mississippi (Lukas Flippo/The Sun Herald via AP)

“It’s very efficient, very tropical rainfall,” said National Hurricane Centre director Ken Graham. “It rains a whole bunch real quick.”

Rising water on Lake Pontchartrain near New Orleans pushed about two feet of water into the first floor of Rudy Horvath’s residence — a boathouse that sits on pilings over the lake. Mr Horvath said he and his family have lived there a year and have learned to take the occasional flood in their stride. They have put tables on the lower floor to stack belongings above the high water.

“We thought it would be pretty cool to live out here, and it has been,” Mr Horvath said. “The sunsets are great.

In Florida, a tornado — the second in two days in the state as the storm approached — uprooted trees and downed power lines south of Lake City near Interstate 75, the weather service and authorities said. There were no reports of injuries.

President Donald Trump agreed to issue an emergency declaration for Louisiana, officials said.