Hurricane Nate gathered strength Saturday as it swept towards the US Gulf Coast after dumping rain heavy that killed at least 28 people in Central America.
New Orleans, which was ravaged by deadly Hurricane Katrina in 2005, and other US Gulf coast cities were under a hurricane warning.
President Donald Trump issued an emergency declaration allowing federal emergency aid to be sent to help mitigate the storm's impact.
Nate's center was located 395 kilometers south-southeast of the mouth of the Mississippi River, the US National Hurricane Center (NHC) said at 1200 GMT.
Its winds swirled at 135 kilometers (85 miles) per hour, making it a Category One hurricane on the five-level Saffir-Simpson scale.
Nate was moving towards the northwest rapidly at 22 miles (35 kilometers) per hour, and is set to make landfall along the central US Gulf Coast late Saturday.
"The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline," the NHC said.
The water was expected to peak at up to 2.7 meters (nine feet) above ground in some areas.
New Orleans issued a mandatory curfew for Saturday from 6:00 pm (2300 GMT), and mandatory and voluntary evacuation orders were issued for certain low-lying areas.
Swells expected to affect northwestern Caribbean land over the weekend "are likely to cause life-threatening surf and rip current conditions," according to US forecasters.
In Mexico, authorities canceled school in seven coastal towns and declared an orange alert for the northern half of Quintana Roo state.
Luis Felipe Puente, Mexico's national coordinator of Civil Protection, recommended "avoiding aquatic, touristic and recreational activities" in Quintana Roo.
"Our greatest threat... is not necessarily rain, but strong winds and storm surge," said New Orleans Mayor Mitch Landrieu.
Unlike Hurricane Harvey, which dumped record amounts of rain while hovering over neighboring Texas for a week, fast-moving Nate was expected to quickly pass along a northerly path.
Louisiana Governor John Bel Edwards warned that while Nate was forecast to be a weak hurricane, it could still cause unexpected damage.
"Anyone in low-lying areas... we are urging them to prepare now," he said.
In the neighboring state of Mississippi, lines formed at gas stations in areas within the potential path of the storm.
Some offshore oil and gas rigs in the Gulf of Mexico were evacuated ahead of the storm's advance.
Nate's tail was still wreaking havoc in Central America, where heavy rains continued causing floods.
Intense rains forced thousands from their homes, uprooted trees, knocked out bridges and turned roads into rivers across a swath of the region on Thursday.
"We were drowning. Thank God (emergency workers) helped us. The river swelled so much it swept away our house, our pigs, our chickens -- it swept away everything," said Bonavide Velazquez, 60, who was evacuated from her home in southern Nicaragua.
Nicaragua bore 13 of the deaths, according to Vice President Rosario Murillo.
In Costa Rica, where a national emergency was declared, 10 people died, including a three-year-old girl, after they were hit by falling trees and mudslides.
Authorities warned of crocodiles that might be roaming after rivers and estuaries flooded.
Three other people were killed in Honduras, and two in El Salvador.
More than 30 people are listed as missing across the region.
The United States is recovering from two major hurricanes: Harvey, which tore through Texas in August, and Irma, which slammed Florida in September.
Another powerful storm, Hurricane Maria, ripped through the Caribbean in late September, devastating several islands, including Dominica and Puerto Rico.
Central America, the Caribbean, Mexico and the southern United States experience an Atlantic hurricane season every year that runs from June to November.
But 2017 is already one of the worst years on record.