The fourth named storm of the season, Debra developed from the interaction between a high-altitude cold low and a lower tropical wave in the Gulf of Mexico.

Debra originated in an upper-level cold-core low pressure system that developed over southwestern Florida in late August 1978.

The low moved southwest towards the Yucatán Peninsula over the next day, as a tropical wave drifted westwards from the Caribbean Sea.

[1] The interaction between the upper-level system and the wave led to the formation of a tropical depression on August 26 around 460 miles (740 km) south of New Orleans.

[1][2] At first the depression drifted westward but, as the western periphery of a high-pressure area weakened, it tracked towards the north and slowly strengthened.

After a reconnaissance aircraft found surface winds of 45 mph (70 km/h) on August 28, the depression was upgraded to Tropical Storm Debra.

[1][2][3] While Debra approached the coast of Louisiana, an additional flight into the system found a drop in surface pressure to 1000 mbar (hPa; 29.53 inHg), as well as peak winds of approximately 60 mph (100 km/h) at 00:00 GMT on August 29.

[1][2][4] Observation stations off the coast recorded sustained winds of 45–50 mph (70–80 km/h) on August 28, as Debra passed 150 miles (240 km) to the west.

[2][4][15] Tornadoes were reported in Memphis, Tennessee; Little Rock, Arkansas; Starkville, Springdale, Cedarbluff and Flora in Mississippi; Livingston and Ascension parishes[30] and north Lafayette in Louisiana.