Why Is the Flooding in Louisiana So Bad?


A man navigates a boat of rescued goats past a partially submerged car after flooding on August 16, 2016 in Gonzales, Louisiana. Image credit: Brendan Smialowski/AFP/Getty Images

Parts of central and eastern Louisiana are recovering from some of their worst flooding in recorded history after a days-long encounter with an unnamed tropical storm, capping a long week of torrential rains along the Gulf Coast that inundated communities from Florida to Texas. The flooding was worse than what many communities see when even the strongest hurricanes make landfall, and it took some folks by surprise because there wasn’t much coverage of the heavy rain until the water started rising. How did this happen? A certain combination of weather events came together just right over the past week to create the devastating flooding in Louisiana, which has left 10 dead and tens of thousands displaced.  

A trough of low pressure—an elongated area of lower air pressure that doesn’t have a closed circulation of winds at the surface—developed over the northeastern Gulf of Mexico on August 6, producing heavy thunderstorms that dropped intense rainfall over western Florida for a couple of days. Some communities north of Tampa, Florida, saw widespread flooding as a result of nearly a foot of rain that weekend. Weather Channel meteorologist Mike Seidel recorded a raft of fire ants clinging together for survival in the Florida flooding—an unpleasant reminder that you should never step foot in floodwater if you don’t have to.

Total observed rainfall between August 7, 2016, and August 14, 2016. The white patches over Louisiana are areas that saw more than 20 inches of rain. Image credit: National Weather Service

The storms didn’t move in a hurry. The disturbance slowly drifted across the northern Gulf Coast for the following week, bringing heavy rain to Louisiana that began on August 10 and didn’t subside for the next three days. The main airport in Baton Rouge recorded 19.24 inches of rain between August 10 and August 13; 11.24 inches fell on August 12 alone, which is just shy of the record for most rain ever recorded in one day since records began there in 1930. The small town of Livingston, about 25 miles east of Baton Rouge, saw more than two feet of rain over the same period of time, picking up nearly 27 inches of rain by the time the skies cleared out.

The sudden onslaught of water shattered years-old records and left tens of thousands of people stranded in cars, homes, and just about wherever they were when the water started to rise. First responders came by boat and helicopter to make thousands of water rescues during the flooding. The Advocate reports that around 1000 people were stranded on Interstate 12 when water inundated the road. The Comite River in Baton Rouge surged from a depth of just two feet on the morning of August 11 to a record-setting depth of 34.2 feet around midnight on August 14, blowing past the previous record high water mark of 31 feet set back in June 2001. The nearby Amite River grew to a record high of 46.2 feet on August 14, breaking a record set in 1983 by nearly five feet.

While the flooding isn’t anywhere near the scale of what New Orleans and southern Mississippi experienced during Hurricane Katrina, it’s still likely going to rank among the most devastating flooding events to hit this area in modern history. This flood was the result of heavy rain—in contrast, the flooding we saw along the coast in Katrina was a storm surge, or the storm’s intense winds pushing sea water inland.

A visible satellite image of the tropical thunderstorms over Louisiana on the afternoon of August 12, 2016. Image credit: NASA

Why did this storm produce so much rain? It was essentially a slow-moving tropical storm without the swirling winds. Meteorologists using weather balloons measured an almost-unprecedented amount of moisture in the atmosphere during the height of the storms, more than what you’d find in most hurricanes. When a thunderstorm formed, it tapped into abundant tropical moisture that was like turning on a faucet in the sky.

Not only that, but the system didn’t move, which allowed rain to fall over the same areas for an extended period of time. The same ridge of high pressure that’s baking the eastern United States in a brutal heat wave helped this system park itself over Louisiana since there wasn’t much wind in the middle and upper levels of the atmosphere to steer the storm elsewhere. The ridge of high pressure also vented the top of the thunderstorms like an exhaust pipe so they could keep regenerating without choking themselves off.

This disturbance had all of the fury of a tropical storm without the pretty name or the title. Unfortunately, even though a storm like this shattered longstanding records and left behind worse flooding in this region than almost any tropical storm or hurricane that’s struck here in modern history, this system didn’t get anywhere near the attention it deserved simply because it didn’t have a name. This storm is an ever-present reminder that we need to focus on the effects of a storm whether or not it has a snappy name we can use as a hashtag. Rain is rain. A flood is a flood. Don’t wait to hear something on the news about a storm heading your way—be proactive about it by always checking your local forecasts and never ignoring a watch or a warning.