Hurricane Irma was the strongest observed in the Atlantic in terms of maximum sustained winds since Wilma and the strongest storm on record to exist in the open Atlantic region. Irma was the first Category 5 hurricane to strike the Leeward Islands on record, followed by Maria two weeks later. The ninth named storm, fourth hurricane, second major hurricane, and first Category 5 hurricane of the 2017 season, Irma caused widespread and catastrophic damage throughout its long lifetime, particularly in the northeastern Caribbean and the Florida Keys. It was also the most intense hurricane to strike the continental United States since Katrina in 2005, the first major hurricane to make landfall in Florida since Wilma in the same year, and the first Category 4 hurricane to strike the state since Charley in 2004. The word Irmageddon was coined soon after the hurricane to describe the damage caused by the hurricane.
A Cape Verde hurricane, Irma developed from a tropical wave near the islands on August 30. Favorable conditions allowed Irma to rapidly intensify into a Category 3 hurricane on the Saffir–Simpson wind scale by late on August 31. However, the storm's intensity fluctuated between Categories 2 and 3 for the next several days, due to a series of eyewall replacement cycles. On September 4, Irma resumed intensifying, becoming a Category 5 hurricane by early on the next day, and acquiring annular characteristics. Early on September 6, Irma peaked with 1-minute sustained winds of 180 mph (285 km/h) and a minimum pressure of 914 hPa (27.0 inHg). Irma was the second-most intense tropical cyclone worldwide in 2017 in terms of barometric pressure, and the strongest worldwide in 2017 in terms of wind speed. Another eyewall replacement cycle caused Irma to weaken back to a Category 4 hurricane, but the storm re-attained Category 5 status before making landfall in Cuba. Although Irma briefly weakened to a Category 2 storm while making landfall on Cuba, the system re-intensified to Category 4 status as it crossed the warm waters of the Straits of Florida, before making landfall on Cudjoe Key on September 10. Irma then weakened to Category 3 status, prior to another landfall in Florida on Marco Island later that day. The system degraded into a remnant low over Alabama and ultimately dissipated on September 13 over Missouri.
The storm caused catastrophic damage in Barbuda, Saint Barthélemy, Saint Martin, Anguilla, and the Virgin Islands as a Category 5 hurricane. The hurricane caused at least 134 deaths: one in Anguilla; one in Barbados; three in Barbuda; four in the British Virgin Islands; 10 in Cuba; 11 in the French West Indies; one in Haiti; three in Puerto Rico; four on the Dutch side of Sint Maarten; 92 in the contiguous United States, and four in the U.S. Virgin Islands. Hurricane Irma was the top Google searched term in the US and globally in 2017.