Hurricane Irma was the costliest tropical cyclone in the history of the U.S. state of Florida, before being surpassed by Hurricane Ian in 2022. Irma also was the first major hurricane to strike the state since Wilma in 2005 and the first Category 4 hurricane to make landfall in Florida since Charley in 2004. Irma developed from a tropical wave near the Cape Verde Islands on August 30, 2017. The storm quickly became a hurricane on August 31 and then a major hurricane shortly thereafter, but would oscillate in intensity over the next few days. By September 4, Irma resumed strengthening, and became a powerful Category 5 hurricane on the following day. The cyclone then struck Barbuda, Saint Martin, and the British Virgin Islands on September 6 and later crossed Little Inagua in the Bahamas on September 8. Irma briefly weakened to a Category 4 hurricane, but re-intensified into a Category 5 hurricane before making landfall in the Sabana-Camagüey Archipelago of Cuba. After falling to Category 3 status due to land interaction, the storm re-strengthened into a Category 4 hurricane in the Straits of Florida. Irma struck Florida twice on September 10 – the first as a Category 4 at Cudjoe Key and the second on Marco Island as a Category 3. The hurricane weakened significantly over Florida, and was reduced to a tropical storm, before exiting the state into Georgia on September 11.

Preparations for the hurricane began nearly a week before it struck the Keys, beginning with Governor Rick Scott declaring a state of emergency on September 4. With both the Atlantic and Gulf coasts of the state threatened, record evacuations ensued with an estimated 6.5 million people relocating statewide. A mandatory evacuation order was issued for all Monroe County—though roughly 25% of residents stayed—and portions of 23 other counties. The large-scale evacuation strained roadways, with gridlock reported along Interstates 75, 95, and Florida's Turnpike. A total of 191,764 people sought refuge in public shelters. All major airports saw disruption of services, resulting in the cancellation of 9,000 flights. Professional and college-level athletics saw substantial schedule adjustments due to the storm.

The storm's large wind field resulted in strong winds across the entire state except for the western Panhandle. The strongest reported sustained wind speed was on Marco Island, while the highest observed wind gust was , recorded near Naples, though stronger winds likely occurred in the Middle Florida Keys. Over 7.7 million homes and businesses were without power at some point – about 73% of electrical customers in the state, making Irma the largest power outage relating to a tropical cyclone in United States history.Why Only Some Hurricanes Cause Massive Power Outages, Urbint Precipitation was generally heavy to the east of the storm's path, peaking at in Fort Pierce. Heavy rainfall – and storm surge, in some instances – caused at least 32 rivers and creeks to overflow, resulting in significant flooding, especially along the St. Johns River and its tributaries. Many homes and businesses were damaged or destroyed, including over 65,000 structures in West Central and Southwest Florida alone. Agriculture was also hit hard, suffering about $2.5 billion (2017 USD) in damage. It was estimated that the cyclone caused at least $50 billion in damage, making Irma the costliest hurricane in Florida history, surpassing Hurricane Andrew; however, Irma was greatly surpassed in this aspect by Hurricane Ian in 2022. The hurricane left at least 84 fatalities across 27 counties, including 12 at a nursing home due to sweltering conditions and lack of power in the hurricane's aftermath.

Background

A tropical wave moved off the coast of western Africa on August 26. The tropical wave eventually developed into the tenth tropical depression of the season west of the Cape Verde Islands, becoming Tropical Storm Irma. Irma then rapidly intensified into a Category 3 hurricane due to warm sea surface temperatures and low wind shear on September 1. The storm oscillated in intensity over the next few days due to drier air. By September 4, it began rapidly intensifying into a Category 5 hurricane. It made landfall twice in Barbuda and Saint Martin, chronologically, at peak intensity on September 6, with maximum sustained winds of 180 mph and a barometric pressure of 914 mbar. The storm's pressure rose slightly before making another landfall in Virgin Gorda on the same day. Irma began to gradually weaken, forming concentric eyewalls and expanding its wind field. As it moved away from the Virgin Islands, it weakened to a Category 4 hurricane and passed south of the Turks and Caicos Islands.

Irma made landfall on Little Inagua in the Bahamas as a high-end Category 4 hurricane on September 8. The hurricane then re-intensified, reaching Category 5 intensity east of Cuba before making landfall in Cayo Romano, Cuba, on September 9. As it moved along the northern coast of Cuba, the eye became cloud-filled and the intensity fell to a high-end Category 2 hurricane. Irma's forward speed slowed and began to move northwestward toward Florida due to a complex steering pattern, which moved around the southwestern edge of the subtropical high and a low-pressure system over the continental United States. Over the Florida Straits, Irma restrengthened and re-attained Category 4 intensity. The hurricane's wind field increased in size, with hurricane-force winds spanning 80 mi and gale-force winds spanning 220 mi before making landfall in Cudjoe Key, Florida, at 13:00 UTC on September 10, as a low-end Category 4 hurricane. The storm weakened to a low-end Category 3 hurricane before making its final landfall in Marco Island, Florida, at 19:30 UTC. Irma accelerated to the north-northwest, weakening due to wind shear, land interaction, and dry air. It passed east of Tampa as a weak Category 1 hurricane before eventually weakening to a tropical storm and exiting the state into Georgia on September 11. It degenerated to a remnant low in Alabama on September 12.

Irma was the first major hurricane to strike the state since Wilma in 2005 and the first Category 4 hurricane to make landfall in Florida since Charley in 2004. Irma was only the second hurricane to hit Florida since Wilma, the other being Hermine in 2016. Due to few very intense hurricanes since Hurricane Andrew in 1992, there was concern that many Floridians never experienced or did not recall experiencing a hurricane as strong as Irma was projected to be at landfall, with significant growth in population and assets during the previous 25 years.

Irma struck the state less than two weeks after Potential Tropical Cyclone Ten had caused the worst flooding seen in western Florida in at least 20 years, which worsened the disaster in the region.

Preparations

Florida Governor Rick Scott declared a state of emergency on September 4. Several local state of emergencies were declared. A total of 100 members of the Florida National Guard were initially placed on duty by Governor Scott to assist in preparations, while all 9,000 troops were required to report for duty by September 8. Officials encouraged residents to stock-up on emergency supplies. The state coordinated with electrical companies for power outages to be restored as quickly as possible, extending resources such as equipment, fuel, and lodging for the approximately 24,000 restoration personnel who had been activated. Governor Scott waived tolls on all toll roads in the state, including on Florida's Turnpike. All state offices were closed from September 8 to 11, while public schools, state colleges, and state universities in all 67 counties were closed during the same period. The Florida Department of Education coordinated with school districts as the need for transportation by school buses and opening shelters arose. By September 9, more than 150 state parks were closed.

Many airports and seaplane bases throughout the state were closed. Nearly 9,000 flights intending to arrive in or depart from Florida were canceled. Along Florida's coasts, the seaports of Port Canaveral, Port of Key West, Port Manatee, Port of Miami, Port of Palm Beach, and Port Everglades, and Port of St. Petersburg were closed, while the ports at Port of Fernandina, Port of Jacksonville, Port of Panama City, and Port of Pensacola were opened, but with restricted access. For the fifth time in its 45-year history, the Walt Disney World Resort was completely closed due to the storm. Disney's Fort Wilderness Resort & Campground closed on September 9 at 2:00 p.m. due to its location in a heavily wooded area of the resort, while the Magic Kingdom, Epcot, Disney's Hollywood Studios, Disney's Animal Kingdom, Blizzard Beach, Typhoon Lagoon and Disney Springs were all closed by 9:00 p.m. on September 9 and remained closed until September 12. Other Orlando metropolitan area theme parks and water parks, including Universal Orlando Resort's Universal's Islands of Adventure, Universal Studios Florida, Universal's Volcano Bay and SeaWorld Orlando Resort and Aquatica Orlando, were also closed. The Kennedy Space Center was closed from September 8 to 15.

Officials from the Environmental Protection Agency (EPA), which had been criticized for its response to Hurricane Harvey, took special measures to inspect and secure hazardous materials, especially at Superfund sites. At the time, the EPA had 54 Superfund sites in Florida. A survey conducted a few years before the hurricane indicated that a storm surge of just could flood Superfund sites in low-lying areas of South Florida, potentially causing toxic waste to enter aquifers used for drinking water.

Watches and warnings

The National Hurricane Center (NHC) issued watches and warnings in Florida as Irma approached the state. At 15:00 UTC on September 7, a hurricane watch was issued for parts of South Florida, from the Jupiter Inlet to Bonita Beach, including the Florida Keys and Lake Okeechobee. The hurricane watch area was upgraded to a hurricane warning at 03:00 UTC on September 8, while a new hurricane watch was issued on the west coast from Bonita Beach to Anna Maria Island and on the east coast from the Jupiter Inlet to the Sebastian Inlet. Twelve hours later, the watches were extended northward on the west coast to the Anclote River and on the east coast to the Flagler-Volusia county line. At 21:00 UTC on September 8, the hurricane watch along the Gulf Coast was stretched to the Suwannee River; the hurricane warning was simultaneously modified to include all areas from Sebastian Inlet southward along the Florida peninsula to Anna Maria Island, as well as the Florida Keys.