Thousands of people were without power as Tropical Storm Gordon made landfall late Tuesday just west of the Alabama-Mississippi border.
The National Hurricane center said Gordon struck about 10 p.m. and the storm is forecast to quickly weaken as it moves inland across Mississippi, Louisiana and into Arkansas through Thursday.
It did not reach hurricane status.
Gordon strengthened some in the final hours as it neared the central Gulf Coast, clocking top sustained winds of 110 kph.
The National Hurricane Center said Gordon's tight core was about 30 kilometres southeast of Biloxi, Mississippi, or about 55 kilometres south of Mobile, Alabama, where heavy rains and winds picked up shortly before nightfall.
More than 27,000 customers are without power Tuesday night as Tropical Storm Gordon began pushing ashore. Those outages are mostly in coastal Alabama and include the western tip of the Florida Panhandle around Pensacola, with a few hundred in southeastern Mississippi.
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The number of outages has been rising rapidly after dark Tuesday night as Tropical Storm Gordon's wind and rain began to take a toll on the Gulf Coast's power grid.
Pensacola International Airport has reported more than 4 inches of rain, the heaviest total reported so far along the Gulf Coast.
Skies quickly turned dark gray as storms overshadowed Mobile, a port city. Metal chairs were lashed together atop tables outside a restaurant in what's normally a busy entertainment district, and a street musician played to an empty sidewalk just before the rain began.
Conditions were expected to deteriorate westward to New Orleans as the stormed closed in on the coast, possibly becoming the second hurricane to hit the region in less than a year.
Families along the coast filled sandbags, took patio furniture inside and stocked up on batteries and bottled water ahead of Gordon.
John and Robin Berry, vacationing on Dauphin Island, Alabama, went to the beach to see the roaring surf before the rain began. Accompanied by their dog Bentley, the couple had to evacuate the beachfront home they had rented for the week because of Gordon, but they didn't go very far.
"There are no dunes and there's no protection, so the realty company we rented from moved us across the street and down so that we would be safe," said Robin Berry.
Visiting from Nashville, Tennessee, the couple planned to stay on the island despite the storm. Katrina cut the narrow island in half more than a decade ago, but John Berry wasn't very worried about Gordon.
"It's awesome. It's so beautiful," he said of the pounding waves.
About 20 miles away on the mainland, dozens of brightly colored shrimp boats were tied up to docks in Bayou La Batre, a seafood town that processes oysters, shrimp and crabs from across the Gulf of Mexico.
The staff at The Hotel Whiskey in Pass Christian, Mississippi only about a block from the Gulf of Mexico were among those carrying out pre-storm preparation rituals. The hotel restaurant planned to stay open Tuesday evening as usual, fortified by sandbags to keep out torrential rains, the manager said.
Gulfport was among communities providing sand and bags to residents, and Kenny Macdonald filled them for himself and older residents.
MacDonald said that while such preparations become all too routine, one must remain wary.
"You don't know what the intensity of the storm is going to be. You don't want to take it lightly, of course," MacDonald said.
A hurricane warning was in effect for the entire Mississippi and Alabama coasts with the possibility Gordon would become a Category 1 storm. The National Hurricane Center predicted a "life-threatening" storm surge of 3 to 5 feet (0.9 to 1.5 metres) along parts of the central Gulf Coast.
Flooding also was a risk. As much as 20 centimetres of rain could fall in some parts of the Gulf states through late Thursday as the tropical weather moves inland toward Arkansas.
Forecasters said it was possible Gordon's winds might meet the 120 kph threshold to be a hurricane before making landfall later Tuesday. The last hurricane to strike the US was Nate last October, coming ashore in Biloxi with 120 kph winds.
Governors in Alabama, Mississippi and Louisiana all declared states of emergency to better mobilize state resources and National Guard troops for the storm. Mississippi shut down a dozen Gulf Coast casinos. Workers on at least 54 oil and gas production platforms were evacuated.
Gordon became a tropical storm Monday near the Florida Keys.
Mayors of barrier islands in the storm's path warned that their communities might get cut off from the mainland.
"When you get the higher waves, water starts splashing across. Sometimes it starts pushing not only water across but debris, logs and things of that nature, which makes it very treacherous to get across," said Jeff Collier, mayor of Dauphin Island, Alabama.
Gordon was poised for only a glancing blow to New Orleans, where Mayor LaToya Cantrell said the city has "the pumps and the power" needed to protect residents.
Authorities issued a voluntary evacuation order for areas outside the city's levee protection system.
Gordon was not the only storm being watched by forecasters. Hurricane Florence was some 3,900 kilometres away from the US, and another potential storm was likely to form not far off the coast of Africa and head east.
The National Hurricane Center said it is way too early to know if either of those storms will have any impact on land.