The Great Flood of June 2018 for the Rio Grande Valley and Coastal Bend of South Texas

A westward-moving upper level shear vorticity axis eased across the Texas coast on 18 June 2018, and deep tropical moisture followed the vorticity axis onto the coast later that day. The moisture was acted upon by a combination of short-wave disturbances to produce four consecutive days of mesoscale convective systems that left more than 1 ft (30.48 cm) of rainfall from the Rio Grande Valley to the Coastal Bend of South Texas by the time the rain ceased on 22 June. For the Rio Grande Valley, the area-wide rainfall was the most since Hurricane Beulah (1967) and for some communities, the highest event total on record.

Back-to-back short-duration torrential rain events on 20 and 21 June over highly populated sections of Hidalgo County, Texas, produced the bulk of the damage and destruction. An estimated 12 to 18 in (30.48 to 45.72 cm) fell in Weslaco and Mercedes early on 20 June, with an estimated hourly rainfall of more than 5 in (12.7 cm). Similar event totals fell between 20 and 21 June across much of the McAllen/Edinburg/Mission Metropolitan Statistical Area (MSA). Each case was considered a 1/500 annual probability event and left many neighborhoods with 3 to 5 feet of water depth, which overwhelmed drainage systems across the region. Rivers and creeks reached moderate to major flood status from the Coastal Bend to the Rio Grande Valley, with some levels among the top ten highest on record.

Preliminary damage assessments indicated more than 22,000 homes, businesses, and public facilities were affected, of which more than 12,000 were considered to be damaged or destroyed, based on Federal Emergency Management Agency definitions. As many as 10,000 vehicles were damaged or considered a total loss. Public property damage exceeded $50 million, and total damage was likely to exceed $250 million.

This presentation will describe the Great Flood of 2018, from an overview of the meteorological conditions that created the situation to the impact, response, and months-long recovery on a large population for which the event was unprecedented.