Hurricane Dennis was an early-forming major hurricane in the Caribbean and Gulf of Mexico during the very active 2005 Atlantic hurricane season. Dennis was the fourth named storm, second hurricane, and first major hurricane of the season. In July, the hurricane set several records for early season hurricane activity, becoming both the earliest formation of a fourth tropical cyclone and the strongest Atlantic hurricane ever to form before August, the latter a title it held for only six days before being surpassed by Hurricane Emily.
Dennis hit Cuba twice as a Category 4 hurricane on the Saffir-Simpson Hurricane Scale, and made landfall on the Florida Panhandle in the United States as a Category 3 storm less than a year after Hurricane Ivan did so. Dennis caused at least 89 deaths (42 direct) in the U.S. and Caribbean and caused $2.23 billion (2005 US dollars) in damages to the United States, as well as an approximately equal amount of damage in the Caribbean, primarily on Cuba.
Hurricane Dennis began as Tropical Depression Four in the southeastern Caribbean Sea on the evening of July 4, the first storm of the season to form away from Mexico and Central America. Almost immediately, it made landfall on Grenada as a tropical depression with 30 mph (48 km/h) winds. On the morning of July 5, it strengthened into Tropical Storm Dennis in the eastern Caribbean; this was the earliest formation of an Atlantic season's fourth storm (by comparison, during the 2004 season, Hurricane Alex formed in early August and Hurricane Charley made landfall in Cuba on August 12). The newly named Dennis began moving rapidly to the west-northwest.