Tropical Storm Cristobal made landfall over southeastern Louisiana on Sunday evening, the National Hurricane Service announced, packing strong winds and rain after triggering early flooding and at least one damaging tornado in Florida.
People waterside communities outside the New Orleans levee system faced urgent calls to evacuate Sunday afternoon.
Water swamped the only road to Grand Isle — the resort barrier island community south of New Orleans where a mandatory evacuation took effect Saturday.
Cristobal packed top sustained winds of 50 miles per hour winds nearing the coast as forecasters warned that the storm would affect a wide area stretching some 180 miles.
President Trump agreed to issue an emergency declaration for Louisiana as the storm approached the coast.
Meanwhile, in Florida, a tornado splintered and uprooted trees and downed power lines south of Lake City near Interstate 75, but there were no immediate reports of injuries.
Rain fell intermittently in New Orleans' famed French Quarter on Sunday afternoon, but the streets were nearly deserted, with many businesses already boarded up because of the coronavirus pandemic.
Daniel Priestman said he didn't see people frantically stocking up as he did before other storms. He said people may be "overwhelmed" by the coronavirus and recent police violence and protests.
They seemed "resigned to whatever happens - happens," he said.
Tropical storm warnings were in effect for most of Sunday from Intracoastal City in Louisiana to the Okaloosa-Walton County line in Florida, the National Hurricane Center said.
Forecasters said some parts of Louisiana and Mississippi were in danger of as much as a foot of rain, with storm surges of up to five feet.
The Louisiana National Guard had dozens of high-water vehicles and rescue boats ready to go across south Louisiana. Three teams of engineers were also available to help assess potential infrastructure failures, the Guard said in a news release.
The Sewerage & Water Board of New Orleans urged residents to avoid underpasses and low-lying areas where water can pool during inevitable street flooding given the city's aging street drainage system had limits.
In Biloxi, Mississippi, a pier was almost submerged by Sunday morning. Squalls with tropical-force winds had reached the mouth of the Mississippi River and conditions were expected to deteriorate, the hurricane center in Miami said.
Jefferson Parish, a suburb of New Orleans, called for voluntary evacuations Saturday of Jean Lafitte, Lower Lafitte, Crown Point and Barataria because of the threat of storm surge, high tides, and heavy rain. Residents were urged to move vehicles, boats and campers to higher ground.
A similar order was issued for several Plaquemines Parish communities. The parish's president, Kirk Lepine, said the order was issued as a precaution.
The National Weather Service said heavy rainfall and the risk of flash flooding will move inland Sunday night.
The Associated Press contributed to this report.