NEW ORLEANS — Flood-weary New Orleans braced Thursday for the weekend arrival of Tropical Storm Nate, forecast to hit the area Sunday morning as a weak hurricane that could further test a city drainage system in which weaknesses were exposed during summer deluges.

In nearby St. Bernard Parish on Louisiana’s southeast coast, authorities ordered the evacuation of areas unprotected by levees. And to the south of New Orleans, in the barrier island town of Grand Isle, officials called a voluntary evacuation.

In Baton Rouge, Louisiana Gov. John Bel Edwards declared a state of emergency. “We do anticipate a direct hit in Louisiana,” Gov. John Bel Edwards said at an afternoon news conference.

Edwards urged residents to ready for rainfall, storm surge and severe winds — and to be where they intend to hunker down by Saturday evening.

“The bottom line for people is: You need to be where you want to be and in the posture you want to be by dark on Saturday,” he said.

Nate formed Thursday in the western Caribbean Sea near Nicaragua. The forecast track had it reaching southeast Louisiana’s early Sunday, although the range of possible landfalls extended from the central Louisiana coast westward into Alabama.

In New Orleans, Mayor Mitch Landrieu also declared a state of emergency.

“Since early August, we have made substantial progress,” Landrieu said of work to upgrade the city drainage system after summer floods. But he warned at an afternoon news conference that extremely heavy rain and storm surge from Nate still could pose flood dangers.

His office outlined steps being taken to improve weaknesses laid bare in the pumping and drainage system after an Aug. 5 deluge led to flooding of homes and businesses in some sections of the city. In the days that followed came revelations of pumps and power-generating turbines that weren’t working, as well as personnel shortages at the Sewerage and Water Board, the agency that runs the drainage system.

The city said 108 of 120 pumps were fully operational Thursday and said 26 backup generators were also in place. Also, the city said efforts to clean thousands of street catch basins had been stepped up, with vacuum trucks dispatched to various areas to suck out thick mud and debris.