The Billion Dollar Louisiana Floods of August 2016: A Synoptic Overview of the "Tropical Cyclone-Like" System and Downstream "Predecessor Rainfall-Like" Events

A very slow moving cyclone impacted the western Gulf Coast and lower Mississippi Valley regions from 11-15 August, 2016, as it gradually pushed onshore. Across portions of Louisiana, rainfall totals of 15-30” (375-750 mm), with locally higher amounts, were observed. The result was catastrophic flooding, with 13 related fatalities, and total economic losses estimated in the 10-15 billion dollar range.

The system was never categorized as a tropical cyclone by the National Hurricane Center, primarily because of relatively weak winds and an ill-defined center of circulation near the surface. Despite this, the cyclone did have some tropical characteristics, including a well-organized circulation and warm-core nature in the mid-troposphere (850-500 hPa). Additionally, over portions of southeastern Missouri, Illinois, and southern Indiana, significant flash flooding on 12-13 August resulted from heavy rainfall episodes that closely resembled Predecessor Rainfall Events (PRE). The Illinois State Fair was severely impacted by flash flooding on 12 August.

Detailed analyses of the large-scale pattern that led to this natural disaster will be shown. Analogs to other excessive rainfall producing tropical cyclones in the region will be presented, along with comparisons to PRE conceptual models. Also, a relatively new satellite dataset (layered precipitable water imagery) will be used to illustrate the differential advection of deep tropical moisture into the Gulf Coast and Mississippi Valley states. Near record precipitable water values were observed over parts of the region.