Forecasters have issued hurricane warnings for parts of the Louisiana coast, as Tropical Storm Barry churns ominously in the Gulf of Mexico.

U.S. President Donald Trump declared a state of emergency in Louisiana Thursday night, authorizing the Department of Homeland Security (DHS) and the Federal Emergency Management Agency (FEMA) to coordinate federal funds and resources to help the state cope with the storm and its aftermath.

The National Hurricane Center expects Barry to strengthen before landfall and hit the coast as a Category 1 storm late Friday or early Saturday. It would be the first Atlantic hurricane of the season.

As of early Friday, Barry was about 170 kilometers southwest of the mouth of the Mississippi River, with top winds at 100 kph and crawling about 7 kilometers per hour. The slow movement is enabling Barry to suck up more moisture and energy from the warm Gulf waters.

New Orleans, which is already dealing with floods from Wednesday's fierce rainstorms, is under a tropical storm warning, increasing the chance of flash flooding. The city of Baton Rouge is also facing threats of flash flooding.

As of Friday afternoon, Barry was on a path toward Morgan City, which is surrounded by water and nearly 140 kilometers southwest of New Orleans.

Forecasters predict the city can expect as much as 51 centimeters of additional rain from Barry, pushing the Mississippi River's crest close to the top of the 6-meter-high levees protecting New Orleans.

Louisiana Gov. John Bel Edwards has already declared a state of emergency and deployed the National Guard.

Mandatory evacuations have been ordered for about 10,000 people living near the stretch of the Mississippi closest to the Gulf. A storm surge warning is in effect for southern and southeastern Louisiana.

Along with heavy rain and strong winds, Barry could bring dangerous storm surges and tornadoes before it moves inland and weakens.