The hurricane was about 400km southwest of Morgan City, Louisiana as it crawled northeast packing 145km/h winds, according to an advisory by the US National Hurricane Center.
The storm was a category one hurricane on the five-step Saffir-Simpson scale.
Early on Wednesday morning, the US National Weather Service warned that conditions were expected to deteriorate throughout the day as the hurricane threatened some coastal areas with a 5-metre storm surge.
"Make sure you have all preparations rushed to completion ASAP!," the service said on X.
"Then, prepare to hunker down & shelter in place through the overnight hours."
The service issued storm surge watches or warnings along the entire Gulf coast of Louisiana, Mississippi and Alabama.
Louisiana Governor Jeff Landry declared a state of emergency in anticipation of the storm that was due to make landfall just west of New Orleans on Wednesday afternoon, warning of torrential rainfall, damaging winds and possible tornadoes.
US President Joe Biden also declared a federal state of emergency for the state in order to expedite any needed relief or rescue efforts.
Several parishes, or counties, on or near the Louisiana Gulf Coast issued mandatory evacuation orders and the state transportation department issued evacuation maps.
The city of New Orleans was distributing sandbags at five sites.
While the NHC expected the storm to max out as a category two before weakening over land with maximum sustained winds of 154 to 177km/h.
With the storm passing in a northeastern direction parallel to the Texas coast on its way to Louisiana, oil and gas producers abandoned many of their Gulf of Mexico platforms, taking offline about a quarter of energy production, the US Bureau of Safety and Environmental Enforcement (BSEE) said on Tuesday.
The storm also stands to test liquefied natural gas (LNG) export plants recently built in the region, which is home to about 15 per cent of US oil production and 2 per cent of natural gas output.
Any major storm near Louisiana evokes memories of Hurricane Katrina, the 2005 storm that devastated New Orleans and surrounding areas, killing nearly 1400 people and causing $US125 billion ($A188 billion) in damage, according to a 2023 hurricane centre report.
