On June 30, 2002, a low-pressure system migrating westward from Florida combined with a flow of deep tropical moisture from the Gulf of Mexico and moved over southern Texas. The system hit a wall of high pressure and stalled over the central and south-central parts of the State. For 8 days, the storm system continued to draw moisture from the Gulf, which triggered several massive storms throughout much of the area. As much as 35 in. of rain fell during the event, with heaviest depths occurring in the Texas Hill Country northwest of San Antonio. Flooding affected about 80 counties in Texas.

Heavy rain also fell in parts of West Texas, including Abilene, where 12-14 in. of rain in the pre-dawn hours of July 6 caused flooding that required numerous evacuations. Heavy rains also caused Lake Brownwood to overflow, causing evacuations and flooding in parts of Brownwood.

The floods caused 12 deaths and damage to about 48,000 homes. Nearly 250 flood rescue calls were reported, more than 130 roads were closed, and thousands of homes and businesses lost electrical power and telephone service. Twenty-four counties were identified by the Federal Emergency Management Agency (FEMA) as Federal Declared Disaster areas—14 counties were eligible for individual assistance and 10 counties for individual and public assistance. Emergency management representatives had not yet assessed the total cost of damages.

The storms produced large volumes of runoff and as many as four flood peaks at each of many streamflow-gaging stations in the Brazos, Colorado, and Guadalupe River Basins. Record flood stages occurred at sites on the Medina River, San Antonio River, Sabinal River, and Nueces River. For the first time since it filled in 1968, Canyon Lake (northeast of San Antonio) poured over its spillway, adding to the flooding in the Guadalupe River. Emergency managers also were concerned about the 90-year-old dam at Medina Lake (west of San Antonio). Medina Lake topped its spillway and rose to within 18 in. of the top of the dam. Areas downstream from the dam were evacuated as a precaution because of the fear of dam failure.