Meteorologists say rainbands from Tropical Storm Barry began to move onshore Saturday.
The National Hurricane Center warns that Barry is likely to bring dangerous storm surges, plus heavy wind and rain conditions.
Maximum sustained winds are 100 kilometers per hour and the storm is moving toward the coastline at seven kilometers per hour.
Residents in New Orleans are fortifying their homes and stocking up on supplies as Barry begins to roll in from the Gulf of Mexico.
City officials have advised residents to shelter in their homes, with the exception of two coastal parishes south of the city, where mandatory evacuations have been ordered.
Tourists had largely left the city Friday. Some airlines canceled outbound flights on Saturday.
New Orleans Residents Shelter in Homes as Tropical Storm Rolls In Storm could trigger more flooding in and around New Orleans
The National Hurricane Center expects Barry to strengthen before landfall and hit the coast as a Category 1 storm. It would be the first Atlantic hurricane of the season.
The main threat from the storm is expected to be its flood potential rather than its high winds. The storm is widely seen as a test of the city's weather defenses put in place following Hurricane Katrina in 2005, which left about 1,800 people dead.
U.S. President Donald Trump declared a State of Emergency in Louisiana Thursday night, authorizing the Department of Homeland Security (DHS) and the Federal Emergency Management Agency (FEMA) to coordinate federal funds and resources to help the state cope with the storm and its aftermath.
Barry's maximum sustained winds Friday night were clocked at 100 kilometers per hour and the storm is expected to drop as much as 60 centimeters of rain in some places, leading to severe flooding.
New Orleans, which is already dealing with floods from Wednesday's fierce rainstorms, is likely to see more flash flooding. The city of Baton Rouge is also facing threats of flash flooding.
As of Friday evening, Barry was on a path toward Morgan City, which is surrounded by water and nearly 140 kilometers southwest of New Orleans.
Forecasters predict the city can expect as much as 51 centimeters of additional rain from Barry, pushing the Mississippi River's crest close to the top of the 6-meter-high levees protecting New Orleans.
Louisiana Governor John Bel Edwards has already declared a state of emergency and deployed the National Guard.
Mandatory evacuations have been ordered for about 10,000 people living near the stretch of the Mississippi closest to the Gulf. A storm surge warning is in effect for southern and southeastern Louisiana.
Along with heavy rain and strong winds, Barry could bring tornadoes before it moves inland and weakens.