NEW ORLEANS -- This low-lying Louisiana city -- built on a crescent-shaped sliver of land surrounded by the mouth of the Mississippi River, Lake Pontchartrain and the Gulf of Mexico -- has long battled water.
But Tropical Storm Barry presents a somewhat unusual threat.
While tropical storms and hurricanes are a risk along the Gulf Coast throughout the summer and fall, Barry comes at a time when the Mississippi River is already swollen from unprecedented late-season flooding.
Normally, flooding on the lower Mississippi River subsides in May. But the wettest 12-month period on record in the contiguous U.S. has drenched the Midwest, so that the Mississippi River has been above flood stage in southern Louisiana for 187 days, beating a 1927 record by nearly two months.
The Mississippi is already more than 16 feet above sea level in New Orleans, according to the National Weather Service in the city. The levees that protect New Orleans from the river are between 20 and 25 feet high.
"Nowhere along the Mississippi River will the levee be overtopped, but this could be a very significant rain event," Louisiana Gov. John Bel Edwards said at a briefing Thursday in New Orleans. "And whether the water is flooding you, whether it comes from the sky or from the river, at the end of the day it doesn't matter -- it presents the same threat."
While forecasters expect a storm surge of 3 to 6 feet across southeast Louisiana, in New Orleans it is expected to be about 3 feet, which means the river would probably peak at 19 feet on Saturday, keeping it from overtopping the levees.
Still, Edwards stressed that much of southern Louisiana was still at risk of major flooding. Two low-lying coastal areas south of New Orleans -- Plaquemines Parish and Grand Isle -- are already under mandatory evacuations.
Poised to become the first tropical system to strike the United States this 2019 hurricane season, Barry could strengthen into a hurricane late Friday before hitting the Louisiana coast early Saturday, according to the National Weather Service.
It is also forecast to move slowly, dumping as much as 10 to 20 inches over southeast Louisiana and southwest Mississippi, with higher amounts in some areas.
"It has the potential to be a huge rainmaker," said Phil Klotzbach, an atmospheric research scientist at Colorado State University. "That is the biggest concern."
On Thursday afternoon, the storm was about 90 miles south of the mouth of the Mississippi River, moving west with maximum sustained wind of 40 mph.
The National Hurricane Center issued a hurricane warning for a 150-mile stretch of the Louisiana coast, from Intracoastal City to Grand Isle.
New Orleans got an inkling of what was ahead early Wednesday when heavy thunderstorms flooded streets across the metro area.
The city's leaders have yet to call for voluntary or mandatory evacuations, but they urged residents Thursday to prepare for the coming deluge by gathering emergency supplies: perishable food to last three days, three gallons of water per person, as well as a week's supply of prescription medications, first aid kits, flashlights, batteries, matches, lighters and a radio.
On Thursday afternoon, the Louisiana National Guard had begun to activate some of the extra 3,000 soldiers and airmen Edwards had authorized ahead of the storm. It had also staged high-water vehicles and boats in more than 20 communities across the state and positioned helicopters to support search and rescue, evacuation and recon missions as needed.
(Jarvie reported from New Orleans and Boxall from Los Angeles. Times staff writer Molly Hennessey- Fiske in Houston contributed to this report.)
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