Hurricane Betsy was an intense, deadly and destructive tropical cyclone that brought widespread damage to areas of Florida and the central United States Gulf Coast in September 1965. The storm's erratic nature, coupled with its intensity and minimized preparation time contributed to making Betsy the first tropical cyclone in the Atlantic basin to accrue at least $1 billion in damage. While the storm primarily affected areas of southern Florida and Louisiana, lesser effects were felt in the Bahamas and as far inland in the United States as the Ohio River Valley. Betsy began as a tropical depression north of French Guiana on August 27, and strengthened as it moved in a general northwesterly direction. After executing a slight anticyclonic loop north of the Bahamas, Betsy proceeded to move through areas of south Florida on September 8, causing extensive crop damage. After emerging into the Gulf of Mexico, the cyclone strengthened and reached its peak intensity equivalent to that of a Category 4 hurricane on September 10 before making its final landfall near Grand Isle, Louisiana, shortly thereafter. Once inland, Betsy was slow to weaken, and persisted for two more days before degenerating into an extratropical storm; these remnants lasted until September 13.

The Saffir–Simpson hurricane wind scale (SSHWS) classifies hurricanes—which in the Western Hemisphere are tropical cyclones that exceed the intensities of tropical depressions and tropical storms—into five categories distinguished by the intensities of their sustained winds. This measuring system was formerly known as the Saffir–Simpson hurricane scale, or SSHS.