The second tropical cyclone to make landfall in the United States in the 2007 Atlantic hurricane season and the fifth named storm of the year, Erin formed in the Gulf of Mexico on August 14 from a persistent area of convection.

[6] Upper-level winds gradually became more beneficial for development, and on August 13 a broad low pressure area formed about 90 miles (140 km) north-northeast of Cancún, Quintana Roo, Mexico.

[7] Late on August 14, a Hurricane Hunters flight into the system reported a small circulation center, but at the time was not well-defined enough to result in the initiation of tropical cyclone advisories.

[11] As it continued northwestward, Erin remained disorganized and failed to strengthen beyond minimal tropical storm status.

[12] At 1200 UTC on August 16 the cyclone made landfall near Lamar, Texas as it weakened to tropical depression status.

[14] Drifting northwestward through Texas, Tropical Depression Erin maintained an area of convection near the center, with its widespread but scattered rainbands dropping moderate to heavy precipitation.

The system turned to the north-northeast on August 18, while heavy bands of thunderstorms continued to rotate around the center of Erin.

[17][18] The Norman, Oklahoma National Weather Service remarked the intensification "[resulted] in what amounts to an inland tropical storm;"[19] at 0930 UTC the system presented an eye-like feature and a spiral rainband, and produced wind gusts of over 80 mph (130 km/h).

[21] Governor Rick Perry activated the National Guard and mobilized emergency personnel to the region expected to be affected by the storm.

[11] As it moved ashore, the storm produced heavy rainfall near and to the or northeast of its path, reaching 11.02 inches (280 mm) at a station in Lockwood.

[35] In Clear Lake City, heavy rainfall collapsed a portion of a grocery store roof, killing one worker and one Coca-Cola merchandiser.

[33] In San Antonio, one body was recovered from a creek and another died after driving into a flooded road and was swept into a drainage ditch in which four others survived.

The weather forced the cancellation of the Hydro Fair as the carnival rides were not safe in heavy rain and high wind.

The 11.94 inches/303.3 mm that fell at Miller became the wettest Missouri rainfall total associated with a tropical cyclone, or its remains, since at least 1972.