A record rain hit Alvin, Texas, in the late ’70s? What caused so much rain?

Dear Tom,
A record rain hit Alvin, Texas, in the late ’70s? What caused so much rain?
— Richard Smith,
Minooka
Dear Richard,
The 43-inch deluge that swamped Alvin, Texas, on July 25-26, 1979, still stands as the heaviest 24-hour rainfall in the U.S. The rain actually fell in just a 10-hour period from 9 p.m. July 25 through 7 a.m. July 26. Alvin, located near the Texas coast south of Houston, was the recipient of torrential rains associated with slow-moving Tropical Storm Claudette.
That rainfall is dwarfed by the world record of 73.62 inches that fell at Cilaos on Reunion Island, east of Madagascar, on March 15-16, 1952.
For comparison, the Illinois record 24-hour rainfall is 16.94 inches recorded at Aurora on July 17-18, 1996, while Chicago’s 24-hour record rainfall is 9.35 inches on Aug. 13-14, 1987.