Hurricane Betsy was an intense 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.

As a developing tropical cyclone, Betsy tracked over the northern Leeward Islands, producing moderate gusts and slight rainfall, though only minimal damage was reported. After tracking over open waters for several days, Betsy had significantly strengthened upon moving through the Bahamas. There, considerable damage occurred, particularly to crops on the archipelago's islands. For the island chain, Betsy was considered the worst hurricane since a tropical cyclone impacted the region in 1929. Widespread power outage and property damage ensued due to the storm's strong winds. Overall, damage on the Bahamas amounted to at least $14 million, and one fatality occurred. From there Betsy tracked westward and made landfall on southern Florida, where it was considered the worst tropical cyclone since a hurricane in 1926. Betsy's strong storm surge inundated large portions of the Florida Keys, flooding streets and causing widespread damage. The only route out of the Keys onto the mainland was cut off by the storm. In the state alone, Betsy caused $139 million in damage and five deaths.

Betsy's most severe impacts were felt in Louisiana, where it made landfall as a powerful Category 4 hurricane. The cyclone propelled damaging storm surge into Lake Pontchartrain, breaching levees in New Orleans and inundating several neighborhoods, most notably the lower Ninth Ward. Strong winds caused widespread power and telecommunications outages across the region. Further inland, effects wrought by Betsy were considerably weaker, though precipitation caused by the storm extended as far northeast as Pennsylvania. Rainfall was primarily beneficial in Arkansas, though localized flooding impacted rice and cotton crops. In Kentucky and Illinois, strong winds caused moderate property damage. By the time the remnants of Betsy moved into the northeastern United States, the storm's winds and rainfall had substantially lessened, and as such resulting wind damage was negligible while precipitation benefited crops. In total, the damage wrought by Betsy throughout its existence equated to roughly $1.42 billion, making it the costliest Atlantic hurricane at the time. In addition the hurricane caused 81 deaths, primarily in Louisiana. After the season, the United States Weather Bureau retired the name Betsy from their rotating lists of tropical cyclone names.