Days of intense rainfall in August 2016 led to widespread flooding in southern Louisiana, as rivers swelled high above their banks and many crested at record-high levels. According to news reports, the floods prompted the rescue of at least 20,000 people and caused at least six deaths. Louisiana’s governor declared a state of emergency on August 12 and a "major disaster" on August 14.
The animation above shows satellite-based measurements of the rainfall as it accumulated over the southern United States. Specifically, it shows rainfall totals every three hours over the span of 72 hours from August 12-14, 2016. These rainfall totals are regional, remotely-sensed estimates, and local amounts can be significantly higher when measured from the ground.
The data come from the Integrated Multi-Satellite Retrievals for GPM (IMERG), a product of the Global Precipitation Measurement mission. The GPM satellite is the core of a rainfall obseQrvatory that includes measurements from NASA, the Japan Aerospace Exploration Agency, and five other national and international partners.
According to Weather Underground, the multi-day rainfall accumulations (more than 20 inches in some places) stemmed from an unusual storm system. The low-pressure system developed a warm core, and counter-clockwise air flow pulled in moisture from warm waters in the Gulf of Mexico and the Atlantic Ocean. In that sense, the storm was similar to a tropical depression, except that surface winds were light.
The system was extremely slow moving. Over a seven-day period, rain totals in southern Louisiana were at least 600 percent of normal, according to the Lower Mississippi River Forecast Center of the US National Weather Service.