It has just become a tropical storm, but Barry is set to spell some serious flooding concerns for New Orleans, from both torrential rain and storm surge.
A storm surge watch is up in the Big Easy, where there is “the potential for 4 to 6 feet above ground” of inundation in areas unprotected by levees. It is 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 — just shy of flood stage, which begins at 17 feet. The official forecast from the National Weather Service calls for the Mississippi River to hit 19 feet at New Orleans, which corresponds to “moderate flooding.” The forecast was just lowered from a 20-foot “major flooding” mark.
“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 is been a landmark year for freshwater flooding in the United States. The National Oceanic and Atmospheric Administration announced Tuesday that the past 12 months had been the wettest in U.S. history, citing nationwide average rainfall 7.9 inches above average. It has also been the rainiest January through June period on record — with bookkeeping dating back 125 years.
The alarming statistics come as no surprise after record flooding plagued spots from Oklahoma to Ohio — and every place in between.
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,” explained Grigsby. “That could lead to a three- or four-foot storm surge and could get up to the levees in the New Orleans metro.”
Media outlets on Wednesday reported the elevation of some levees along the Mississippi River in New Orleans are even below 20 feet and could be topped by the predicted surge. But the New Orleans Advocate wrote 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 Advocate 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. We don’t get too many July hurricanes here,” Grigsby said.
The official National Hurricane Center forecast calls for a Category 1 system at landfall, but there is an outside chance ample fuel and favorable atmospheric conditions could allow the fledgling storm to intensify a little more than expected. Or it might not even reach hurricane-strength and remain a tropical storm.
Some say that the system’s hesitancy to get organized could be a good sign, potentially sparing New Orleans the worst of any storm surge 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.”
It is not just the coastal flood threat that will pose a danger to New Orleans. Freshwater flooding could prove extremely problematic if persistent rain bands pass over the city repeatedly.
A rare “flash flood emergency” was issued Wednesday morning as a tropical deluge drenched the city with five to seven inches. In just a few hours’ time, 6.27 inches came down at the New Orleans Downtown Heliport, flooding homes and businesses and leaving many areas below water.
Just 24 hours later, the beleaguered city of 400,000 is under a flash flood watch again, the National Weather Service predicting “total rainfall accumulations of 10 to 15 inches” with isolated spots exceeding 20 inches.
“That would completely overwhelm the city’s pumping capacity,” warned Grigsby. Either type of flooding — from the saltwater surge or the extreme rainfall — would alone be enough to spell significant problems. Coupled together, it is looking like a memorable event will soon unfold.
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,” Grigsby said.
An obscene amount of moisture is present for storms to work with amid an atmosphere primed for torrential downpours. A dew point of 82 degrees was measured this morning 70 miles southwest of the Mississippi Delta.
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.
As if that was not bad enough, New Orleans found itself under a tornado warning Wednesday as a waterspout swirled dangerously close over Lake Pontchartrain. More could follow. “We’re in that prime area again,” cautioned Grigsby. “We’ll be watching tornadoes or waterspouts into Saturday.”