Tropical Storm Barry is causing flood concerns for New Orleans because of torrential rain and storm surge.

A storm surge watch is up in the Big Easy, where there is "the potential for 4-6 feet above ground" of inundation in areas unprotected by levees. It's a dangerous scenario within which the storm-driven water rise will coincide with Mississippi River levels already running well above normal, tipping the scales to produce flooding.

As of sunrise Thursday, the river was at 16.16 feet; flood stage begins at 17 feet. The official forecast from the National Weather Service for the Mississippi River was just lowered from a 20-foot "major flooding" mark in New Orleans to 19-foot "moderate flooding."

"The Mississippi is already at a fairly high flood stage going into this," said Phil Grigsby, a meteorologist at the National Weather Service office in New Orleans. "Typically this time of year, it would be below 10 feet, since spring flooding would have normally stopped by now. But it's a lot higher thanks to this year's flooding in the Midwest and Plains states."

It's been a landmark year for freshwater flooding in the United States. The National Oceanic and Atmospheric Administration announced Tuesday that the past year had been the wettest in U.S. history, citing nationwide average rainfall 7.9 inches above average. It's also been the rainiest January through June; such bookkeeping began 125 years ago.

Record flooding has plagued spots from Oklahoma to Ohio recently. Now, the swollen Mississippi is on the verge of overrunning protective levees, which in New Orleans are as low as 20 feet. "If the storm does end up intensifying like we're forecasting, we could get surge up the river," said Grigsby. "That could lead to a 3- or 4-foot storm surge, and could get up to the levees in the New Orleans metro."

Media outlets on Wednesday reported that the elevation of some levees along the Mississippi River in New Orleans are below 20 feet and could be topped by the predicted surge. The Times Picayune reported Thursday that the Army Corps of Engineers disputed those figures and said they are at least "between 20 and 21 feet," which is above the predicted river level.

Still, The Times Picayune reporting found there are "some weak spots in the area's defenses" that could let water through and that areas outside of the levee protection may contend with substantial storm surge flooding.

"It's definitely a tough forecast, but it's interesting, too," said Grigsby. "We don't get too many July hurricanes here."

The official National Hurricane Center forecast calls for a Category 1 system at landfall, but there's an outside chance that ample fuel and favorable atmospheric conditions could allow the fledgling storm to intensify more than currently expected.

Some say that the system's lack of cohesion could be a good sign, potentially sparing New Orleans from devastating flooding.

"The longer it takes Barry to develop, the less threat we can expect from salt water flooding," wrote Hal Needham, founder of Marine Weather and Climate. "A storm that is rapidly strengthening just before landfall will push less storm surge ashore than a one that held its intensity farther out. This is good news, as Barry has struggled to organize, and may run out of time to generate a large storm surge."

Rain also poses a threat to the city.

A rare flash-flood emergency was issued Wednesday morning as a tropical deluge drenched the city with 5 to 7 inches of rain; 6.27 inches came down at the New Orleans Downtown Heliport over a few hours, flooding homes and businesses, leaving many areas underwater.

Just 24 hours later, the beleaguered city of 400,000 people is under a flash-flood watch again as the National Weather Service predicts "total rainfall accumulations of 10 to 15 inches" with isolated spots exceeding 20 inches.

"That would completely overwhelm the city's pumping capacity," Grigsby said. Either type of flooding - from the saltwater surge or the extreme rainfall - would alone be enough to bring significant problems.

The Weather Service's Weather Prediction Center took the unusual step of issuing a "high risk" of flash flooding for the New Orleans area for Saturday - three days in advance.

"We could be talking flooded homes, cars, and businesses," said Grigsby.

Along with the storm surge and heavy rain could come a buffeting wind. Sustained winds of 25 to 35 mph gusting to 70 mph are forecast, with the center of Barry likely to drift a bit west of New Orleans.

New Orleans was also under a tornado warning Wednesday as a waterspout swirled over nearby Lake Pontchartrain. More could follow. “We’re in that prime area again,” said Grigsby. “We’ll be watching tornadoes or waterspouts into Saturday.”