Flash Flood — Willacy, Texas

2020-07-25 to 2020-07-26 · near Port Mansfield, Willacy, Texas

Event narrative

Reports of high flowing water blocking passage along SR-186 just west of Port Mansfield were received during the evening of July 25th, when feeder bands into the eastern semicircle of then-Tropical Storm Hanna dropped an additional 4 to 8 inches of rainfall into central and eastern Willacy County. Other flooding was noted in poor drainage locations of Raymondville, and there was an unknown amount of field flooding in eastern Willacy County due to an estimated 11 to 13 inches of rainfall through the duration of the event, which began during the mid afternoon of July 25th.

Water depths of 2 to 3 feet were likely in some areas, though specifics were unknown. A known poor drainage location at an apartment complex in south Raymondville had up to 3 feet of water depth in parking areas, blocking access to the facility. Other flood related damage in central Willacy County was minimal. In Port Mansfield, where nearly 15 inches of rain fell, including 9 inches in initial inner eyewall bands on July 25th, sandy soil and antecedent dry conditions kept flooding to a minimum.

Crop damage from flooding rain was significant in Willacy County, including a heavy loss of cotton lint (or bolls) which were destroyed by the flood. Estimates suggest that $36 million in cotton crop was lost from Hanna's flooding rains.

Property damage from flood waters was calculated using NCEI's total dollar damage estimate (divided among the affected counties by local storm data experts). Total property damage from flood waters for Willacy County was $5.98 million.

Wider weather episode

Hurricane Hanna, the 2020 Atlantic season's first Hurricane, made landfall along the unpopulated Padre Island National Seashore on the mid-Kenedy County coastline as a Category 1 storm at around 5 PM Central Time Saturday, July 25th, carrying sustained 90 mph winds with gusts over 100 mph in a small portion of the inner eye wall. The hurricane spun slowly but steadily into southern Kenedy and northern Hidalgo County through just after midnight on the 26th, then through Starr County as a Tropical Storm before moving into Tamaulipas before daybreak and eventually near Monterrey, Nuevo Leon, by noon before dissipating during the evening of the 26th. Following the passage of the inner eye wall, broad feeder bands of torrential rains and gusty tropical storm force winds continued through the mid to late morning hours of July 26th, slowly migrating from east to west across the populated Rio Grande Valley.

Other than storm surge flooding, which peaked just north of Baffin Bay on the Kleberg and Nueces County coast near Corpus Christi, Hanna's memory for the Rio Grande Valley will be flooding rainfall, power outages, and an array of damage to poorly constructed buildings, from minor roof damage to complete demolition. Between 8 and 15 inches of rain fell from Port Mansfield to Harlingen, and along Interstate Highway 2 out through Mission and Sullivan City. The combination of high rainfall, locally high rainfall rates, and poor drainage left between 18 inches and four feet of water depth in many areas, most commonly from western Cameron through southeastern Hidalgo County, as well as a separate pocket in the Mission/La Joya/Sullivan City area. The rainfall wiped out 95% of the region's cotton crop; the combination of crop loss and production loss was more than one third of a billion dollars alone ($366 million)...most of which was in the Rio Grande Valley region.

At the peak of the storm, 250 thousand electric customers were without power, including all of Willacy County. Though storm surge was cut short by strong westerly flow across Cameron County, radiating swells did produce a notable surge of 3 feet or greater (estimated) from near Port Mansfield through Kenedy County. When the damage and economic loss is counted to infrastructure and agriculture combined, it is likely that Hanna cost at least one billion dollars across the Rio Grande Valley and the Deep S. Texas ranch country.

View location on OpenStreetMap → (26.5270, -97.5095)

Source: NOAA Storm Events Database, event_id 914438. Narrative written by the NWS forecast office that issued the report.