Hurricane Nate has strengthened slightly as it churns through the Gulf of Mexico, threatening to hit the US central Gulf Coast as a Category 2 storm after killing at least 25 people in Central America.
The outer bands of the hurricane were expected to batter parts of the US Gulf Coast with tropical storm-force winds on Saturday evening, with the centre of the storm forecast to make landfall overnight, said US National Hurricane Centre spokesman Dennis Feltgen.
Major shipping ports across the central US Gulf Coast were closed, as Nate intensified and storm surges of up to 3.74 metres were expected at the mouth of the Mississippi River.
The Category 1 hurricane, the weakest on a five-category scale used by meteorologists, was expected to strengthen to Category 2 before making landfall, according to the National Hurricane Center (NHC).
It was expected to strike between Slidell, Louisiana, and Alabama's Mobile Bay, Alabama Governor Kay Ivey said in a message on Twitter.
It was forecast to veer to the northeast after hitting the coast, a path that would cut through Alabama. Ivey urged residents in areas facing heavy winds and storm surges to take precautions, saying Alabama could be the worst-hit.
As Nate approached, New Orleans, 48 km southwest of Slidell and is the largest city in Louisiana, evacuated some residents from areas outside its levee system.
US Air Force and National Oceanic and Atmospheric Administration aircraft detected that Nate strengthened slightly as it passed over the Gulf of Mexico, according to the NHC.
A state of emergency was declared for more than two dozen Florida counties and for the states of Alabama, Louisiana and Mississippi.
The storm doused Central America with heavy rains on Thursday, killing at least 12 people in Nicaragua, nine in Costa Rica, two in Honduras and two in El Salvador.
Thousands were forced to evacuate their homes and Costa Rica's government declared a state of emergency.
Costa Rican President Luis Guillermo Solis urged residents to remain vigilant, noting rains would likely resume.
In Honduras, residents wondered whether they would have to flee. Norma Chavez and her two children anxiously watched a river rise outside their home in Tegucigalpa, the capital.