All year long, the lower Mississippi River has been stuck at high levels, especially in Louisiana. A developing tropical system will likely push storm surge up the Mississippi River in the coming days, possibly causing the river to rise to 19 feet at the Carrollton Gauge in New Orleans by Friday or Saturday, July 12 or 13. This is two feet above official flood stage, but between one and three feet below the top of earthen levees and floodwalls in the area, according to the National Weather Service.
South of the western Florida Panhandle, a broad low pressure cell has formed in the northern Gulf of Mexico. The cell spread heavy rain into New Orleans today (July 10), flooding streets and buildings. The National Weather Service (NWS) received rainfall reports exceeding 6 inches in parts of the Big Easy. Unfortunately, there could be repeats of this through the rest of the week.
Formerly known as “Invest 92L,” the low has been renamed “Potential Tropical Cyclone Two.” The National Hurricane Center (NHC) is forecasting the storm to evolve into a tropical depression by Thursday morning, strengthening into Tropical Storm Barry by Thursday night. Then, it could make landfall in southwestern Louisiana on Saturday, July 13, possibly as a Category 1 hurricane. The NHC is confident that this system will become a tropical depression or Tropical Storm during the next few days, pinning the chances at 100 percent as it moves into a boiling Gulf, in a manner of speaking, where waters that have warmed well into the 80s.
The Mississippi River in New Orleans has never been so high for so long. If the storm proceeds according to the latest NHC outlook, the storm would create an unprecedented situation in New Orleans – a cyclone-driven storm surge of two to three feet up a river running very high, lifting the water in the Mississippi River nearly to the top of the levees. At 19 feet above sea level, it would be the highest crest for the river in New Orleans since 1950.
The U.S. Army Corps of Engineers, known as “the Corps,” has never had to prepare for the combined assault of a tropical storm and a high-water event on the river, but it’s now making plans to essentially fight a battle on two fronts.
“We have had high-water events in hurricane season but we’ve never had an elevation forecast like this,” Corps spokesman Ricky Boyett told nola.com on Tuesday.
This has not typically been a problem for New Orleans during tropical events because they tend to arrive late in the summer when the river is low. Over the past 50 years, five storms have sent surges of seven feet or more up the Mississippi, most of them at low water levels. If a surge that big hit today, the river would overflow its banks and flood the city.
Hurricane Katrina, for example, sent 13 feet of surge up the Mississippi, but the river was at just three feet above sea level before the storm. Today it’s at 16 feet. The river levees are built to withstand storm surge on the assumption that tropical systems would coincide with low river levels. With the Mississippi possibly up to 17 feet by Friday, even a small surge could cause big problems.
Despite the threat, Boyett said at this point the Corps is not concerned about how the system will hold up.
“Right now we’re pretty confident in the system,” Boyett added. “It’s doing well, it’s holding up pretty well. We’re not seeing any areas of concern.”
The Corps is planning for the worst and hoping for the best, urging people to begin their own preparations now. The possible silver lining – the latest forecast indicates the rise in water would be brief. On Sunday, the river should return to 16.4 feet in New Orleans, and then remain fairly steady.
During a meeting of the U.S. House of Representatives Water Resource and Environment Subcommittee today, U.S. Rep. Garret Graves (R-Louisiana) warned about the requirements for future Water Resources Development Acts, stating that the tropical system brewing in the Gulf would cause “overtopping” of the flood waters that continue to pass through the lower Mississippi from the Midwest. Graves, whose district encompasses Baton Rouge, noted that 1.3 million cubic feet of water per second are passing through that portion of the Mississippi River system. He said the rainfall projections from the tropical storm could breach the levees.
Keep in mind that it’s difficult to pinpoint where the worst weather may occur until the broad low pressure system turns into a more compact, circular system with a center, such as a tropical depression or Tropical Storm. The storm’s rain-making potential comes from indications that it will be moving fairly slowly along its path as it draws in a huge amount of moisture from warm Gulf air. Also, there’s not much wind shear in the upper atmosphere. This means thunderstorms developing around the center of circulation have little chance of being torn apart over the next few days, helping the system to become more organized.
Portions of the central Gulf Coast and nearby inland communities could get slammed with six to 12 inches of total rainfall through early next week, with isolated pockets of up to 18 inches. This, paired with storm surges of three to five feet, have led the NHC to issue the following alerts as of 2:00 p.m. Eastern time today:
• Storm Surge Watch from the mouth of the Pearl River to Morgan City, Louisiana.
• Tropical Storm Watch from the mouth of the Mississippi River to Morgan City, Louisiana.
A Storm Surge Watch means there is a possibility of life-threatening inundation for the next 48 hours due to rising water moving inland from the coastline. A Tropical Storm Watch means that tropical storm conditions, including sustained winds of 39 to 73 mph, are possible within 48 hours. Other Watches, as well as Warnings will be issued as the storm takes shape.
Any more flooding could lead to multiple closures along the I-10 and I-12 corridors, causing delays in freight movement at times for the rest of the week. The storms could slow down shipments into and out of the ports of New Orleans and Baton Rouge. Also, Exxon Mobil Corp (NYSE: XOM) announced today that it has removed non-essential staff from three U.S. Gulf of Mexico platforms, but expected a storm forming in the Gulf to have little effect on its oil and gas production. Company officials said they were prepared to evacuate its remaining workers from the platforms and could adjust operations if needed. The evacuated platforms include the Lena facility, which Exxon is decommissioning.
The National Guard is moving high-water vehicles into place along the Mississippi River in southeastern Louisiana, as well as setting up command posts along coastal Louisiana. The Coastal Protection and Restoration Authority (CPRA) is monitoring 163 floodgates and anticipates some of those will be closed.
At a campaign event in Lake Charles on Tuesday, Louisiana Governor John Bel Edwards said he would suspend the rest of the stops on his RV tour throughout the state and head back to Baton Rouge to prepare for the potentially severe weather. The governor declared a state of emergency earlier today. He is strongly encouraging everyone in the path of the potential storm to take the situation seriously.