During the time-frame August 12-14, 2016, the boot area of the state of Louisiana, northwest of New Orleans, was subject to rainfall of over 30". This produced major flooding that, as of August 20, killed 13 people and inflicted over one billion dollars of damage to thousands of homes and businesses. The slow, westward-moving weather system responsible for this devastation will be shown to have both tropical and non-tropical characteristics, along with huge amounts of precipitable water drawn up from the 87-degree water of the Gulf of Mexico. The difficulty of forecasting the system will be discussed.