Nate killed at least 23 people as it passed through Nicaragua, Costa Rica and Honduras as a tropical storm.
It has since strengthened to a Category 1 hurricane which, though not as strong as last month's Maria and Irma, will still bring strong winds and surges.
A hurricane warning has been issued for parts of the Gulf Coast from Louisiana to Alabama, amid warnings of life-threatening storm surge flooding.
Louisiana Governor John Bel Edwards has declared a state of emergency ahead of the hurricane, which is due to make landfall on Saturday night local time.
He said more than 1,000 National Guard troops had been mobilised with a number sent to New Orleans to monitor the drainage pumps there. "Anyone in low-lying areas... we are urging them to prepare now," he said.
A mandatory curfew from 18:00 (23:00 GMT) is in place in New Orleans.
"Our greatest threat... is not necessarily rain, but strong winds and storm surge," the city's Mayor Mitch Landrieu said.
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