The central coast of the Gulf of Mexico was under a hurricane warning after Tropical Storm Gordon moved across the Gulf on its way toward landfall along the Mississippi coast Tuesday night.

The National Weather Service issued a hurricane warning from the mouth of the Pearl River, which divides Louisiana and Mississippi, to the Alabama-Florida border. Dozens of schools in Louisiana and Mississippi were closed as a precaution after Gordon became a tropical storm late Monday afternoon.

"The storm is moving," Mississippi Gov. Phil Bryant said at a news conference Tuesday afternoon. "What we do not want is for it to loiter out over the warm water and then strike our coast."

The Mississippi cities of Gulfport, Long Beach and Biloxi ordered mandatory evacuations of their harbors and marinas, and the U.S. Coast Guard temporarily closed the ports of New Orleans; Mobile, Alabama; and Pascagoula, Mississippi.

Louisiana Gov. John Bel Edwards said his state would likely miss the worst of the storm, but he encouraged residents to remain vigilant and prepared. He issued a state of emergency and authorized the activation of 200 National Guardsmen to be positioned in southeastern Louisiana.

"We still have some nasty weather headed our way," Edwards told reporters, adding that the state could expect winds of 40 mph to 70 mph. "We're not out of the woods."

"We are going to always prepare for the worst and pray for the best," Guy McInnis, president of St. Bernard Parish, Louisiana, told NBC affiliate WDSU of New Orleans as dozens of boaters and fishers cleared out of Shell Beach.

At 8 p.m. ET, Gordon's top sustained winds were at 70 mph — just short of Category 1 hurricane status — with tropical storm-force winds extending 80 miles from the center. It was about 75 miles southeast of Biloxi, Mississippi, and was moving northwest at 14 mph.

Gordon should weaken rapidly as it heads inland, but it's expected to produce rainfall of 4 to 8 inches from the western Florida Panhandle to southern Arkansas, through Thursday night, with isolated maximums of a foot, the hurricane center said.

The town of Bayou La Batre, in Mobile County, Alabama, was one of many coastal municipalities that issued voluntary evacuation advisories as Gordon approached.

"A lot of folks live in the low-land areas, and we don't want anyone getting caught up in that," Mayor Terry Downey told NBC affiliate WPMI of Mobile. "They need to know that with the surge coming, they could be trapped."

If Gordon becomes a hurricane, it will be the first Atlantic hurricane to make landfall in the United States since Nate last October. Nate had weakened sharply by time it hit the mouth of the Mississippi River, and Ray Coleman, a spokesman for the Mississippi Emergency Management Agency, warned residents not to get complacent.

"My worry is that people might get hurricane amnesia, where they feel like, 'Oh, last year wasn't so bad,'" Coleman told NBC affiliate WLBT of Jackson. "My thing is, no two storms are alike. Just because you made it through Hurricane Nate last year doesn't mean that this one will be the same."

As the Gulf Coast prepared for Gordon, another storm was brewing in the Atlantic: Hurricane Florence formed Tuesday and was about 1,300 miles east of the Northern Leeward Islands, according to the National Hurricane Center.

Early projections showed Florence — the third hurricane of the 2018 Atlantic hurricane season — weakening as it headed north, and no hazards to land were expected, the National Hurricane Center said.