Historic August flood caused by ‘seemingly innocuous’ disturbance, Louisiana’s climatologist says

    Louisiana State Climatologist Barry Keim described the historic August flood that devastated much of south Louisiana as an incredibly rare event that began as a “seemingly innocuous” disturbance, or tropical wave.

    “It’s very unusual to have a flood event produced by a tropical wave,” Keim says. “This is one we’ll be studying for a long time.”

    At today’s Press Club of Baton Rouge luncheon, Keim presented a series of weather maps depicting the disturbance as it moved along the Gulf Coast from Florida to Louisiana.

    From Aug. 3-7, the slow-moving tropical wave sat over Florida. The disturbance became more organized on Aug. 8 as it moved west along the coast, and by Aug. 9, Keim says, it probably should have been classified as a tropical depression. The system then crept into the greater Baton Rouge area on Thursday night, Aug. 11, and rain fell for 32 straight hours.

    To be classified as a 1,000-year flood event, 21.3 inches of rainfall is required, Keim says. Some areas in the Baton Rouge area far exceeded that.

    Watson received a whopping 31.39 inches of rain. The Brownfields area saw 26.8 inches, and Denham Springs had 25.5 inches. Keim says nine recording stations exceeded the 1,000-year flood mark. It was the heaviest rainfall on record in the history of Louisiana.

    “Not only did we beat the record—we crushed it,” Keim says.

    A flood of this magnitude originating from a small tropical wave is very unusual, Keim says, but the high moisture in the atmosphere from the Gulf of Mexico and the high humidity enabled the system. It was able to take the moisture in the atmosphere and bring it to the ground, he says.

    Some question whether global warming influenced recent weather events in Louisiana, but Keim wouldn’t make that connection. The erratic weather does seem consistent with climate change, he says, but he can’t attribute this flood event, or even the whole year of weather events, to climate change.

    “No single event tells us anything about climate change or global warming,” Keim says.

    After the August flood, many are on edge about the potential for more unfortunate weather in the midst of hurricane season. Keim says five to eight hurricanes are predicted this year, and two to four of them are expected to be major hurricanes.

    The state is watching one storm in particular, now known as Tropical Depression 9, which began moving into the southeastern Gulf of Mexico this morning. The storm is expected to turn west-northwest as it initially enters the Gulf before taking a sharp cut back toward Florida, according to the National Weather Service.

    “Right now, it doesn’t seem like a serious threat,” Keim says, “but I admit it is unnerving.”

    —Annie Ourso

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