Walter Augier (L) and Jhon M. fish as rain and wind are whipped up by Tropical Storm Gordon on September 3, 2018 in Miami, Florida

Tropical Storm Gordon gained strength as it moved steadily toward the US Gulf Coast Tuesday, on track to make landfall just east of New Orleans with hurricane force winds.

Authorities declared a state of emergency in the "Big Easy"—devastated in 2005 by mega Hurricane Katrina—and encouraged people living outside its levee system to evacuate voluntarily.

The Miami-based National Hurricane Center (NHC) said Gordon, which formed near the upper Florida Keys Monday, was 190 miles southeast of the mouth of the Mississippi River at 1200 GMT.

A was in place from the mouth of the Pearl River, on the Louisiana-Mississippi state line, to the Alabama-Florida border to the east.

At 1200 GMT, the storm was moving on a northwesterly track at a speed of 15 miles per hour, packing maximum sustained winds of 65 miles per hour (100 kilometers per hour) that extended up to 80 miles from the storm's center.

"The center of Gordon will move across the eastern Gulf of Mexico today, and will approach the north-central Gulf Coast within the warning area late this afternoon or evening, and move inland over the lower Mississippi Valley tonight or early Wednesday," the NHC said in a statement.

Up to eight inches of rain could fall across the Gulf states. Meanwhile, warnings of a "life-threatening" storm surge of up to five feet were in place across a stretch of the Louisiana and Alabama coastline east of New Orleans.

"The deepest water will occur along the immediate coast near and to the east of the landfall location, where the surge will be accompanied by large waves," the NHC said.

The NHC added it expects "rapid weakening" once Gordon makes landfall.