Hurricane Irene was a large and destructive tropical cyclone which affected much of the Caribbean and East Coast of the United States during late August 2011. The ninth named storm, first hurricane, and first major hurricane of the 2011 Atlantic hurricane season, Irene originated from a well-defined Atlantic tropical wave that began showing signs of organization east of the Lesser Antilles. Due to development of atmospheric convection and a closed center of circulation, the system was designated as Tropical Storm Irene on August 20, 2011. After intensifying, Irene made landfall in St. Croix as a strong tropical storm later that day. Early on August 21, the storm made a second landfall in Puerto Rico. While crossing the island, Irene strengthened into a Category 1 hurricane. The storm paralleled offshore of Hispaniola, continuing to slowly intensify in the process. Shortly before making four landfalls in The Bahamas, Irene peaked as a 120 mph (190 km/h) Category 3 hurricane.

Thereafter, the storm slowly leveled off in intensity as it struck the Bahamas and then curved northward after passing east of Grand Bahama. Continuing to weaken, Irene was downgraded to a Category 1 hurricane before making landfall on the Outer Banks of North Carolina on August 27, becoming the first hurricane to make landfall in the United States since Hurricane Ike in 2008. Later that day, the storm re-emerged into the Atlantic from southeastern Virginia. Although Irene remained a hurricane over water, it weakened to a tropical storm while making yet another landfall in the Little Egg Inlet in southeastern New Jersey on August 27. A few hours later, Irene made its ninth and final landfall in Brooklyn, New York City. Early on August 29, Irene transitioned into an extratropical cyclone while striking Vermont, after remaining inland as a tropical cyclone for less than 12 hours.

Throughout its path, Irene caused widespread destruction and at least 49 deaths. Damage estimates throughout the United States are estimated near $13.5 billion, making Irene one of the costliest hurricanes on record in the country. In addition, monetary losses in the Caribbean and Canada were $830 million and $130 million respectively for a total of nearly $14.2 billion in damage.

On August 15, 2011, a tropical wave exited the coast of West Africa and emerged into the Atlantic Ocean, characterized by a distinct low-level cyclonic rotation and deep tropical humidity. It remained well-defined while moving steadily westward for several days to the south of the Cape Verde Islands, although at the time any notable convection occurred well to the southwest of its axis. As the wave distanced itself from the islands, development of thunderstorms and showers in its proximity continued to remain scarce, and it became rather broad in appearance. On August 19, the convective structure began to show signs of organization as the associated atmospheric pressure lowered, and with a progressively favorable environment situated ahead of the wave its chances of undergoing tropical cyclogenesis markedly increased. The strong thunderstorm activity continued to become more pronounced around the main low-pressure feature. By August 20, the National Hurricane Center noted that tropical cyclone formation was imminent as the wave neared the Lesser Antilles, and a reconnaissance aircraft confirmed the presence of a small surface circulation center just southwest of a burst of vigorous convection and unusually high sustained winds, indicating sufficient organization for the cyclone to be upgraded into Tropical Storm Irene at 23:00 UTC that day.

Irene was positioned about 190 mi (310 km) east of Dominica in the Lesser Antilles when it was classified and named, along weakening high pressure over the west-central Atlantic, inducing a roughly west-northwestward path for most of its journey through the eastern Caribbean. Its mid-level circulation continued to become better established as hints of pronounced banding features curved north of the surface center. On August 21, the surface center reformed closer to the deepest convection; furthermore, an anticyclone aloft provided supportive outflow over the cyclone. With the improved structure, as well as light wind shear and high sea surface temperatures, Irene was forecast to strengthen to near hurricane force prior to landfall in Hispaniola. Over the subsequent day (August 22), while passing near the island of Saint Croix in the U.S. Virgin Islands, Irene traced toward Puerto Rico, more northward than initially expected, where it underwent a considerable increase in strength and organization. Hours later, Irene moved ashore, approaching from the southeast near Punta Santiago, Humacao, Puerto Rico, with estimated sustained winds of 70 mph (110 km/h). Despite the storm's interaction with land, radar imagery showed a ragged eye-like feature, and Doppler weather radar data indicated wind speeds in excess of hurricane force. Just after its initial landfall, Irene was accordingly upgraded to a Category 1 hurricane, the first of the 2011 Atlantic hurricane season.

With the hurricane then situated just north of the mountainous coast of Hispaniola, the storm deepened little after reemerging over water, and any additional organization during the rest of the day was gradual. After briefly weakening on August 23, however, Irene began to develop a distinct eye encircled by an area of deepening convection the next morning. Moving erratically through the southeast Bahamas over very warm waters, Irene quickly expanded as its outflow aloft became very well established; the cyclone intensified into a Category 3 major hurricane as it recurved toward the northwest along a weakness in the subtropical ridge. The cyclone subsequently underwent a partial eyewall replacement cycle, which resulted in some reduction in its winds. Although a distinct eye redeveloped for a few hours, it obscured once again soon thereafter; Irene was unable to recover from the cycle, with no further significant intensification expected thereafter.

Early on August 27, Irene further weakened to a Category 1 hurricane as it approached the Outer Banks of North Carolina. At 7:30 am EDT (11:30 UTC) on the same day, Irene made landfall near Cape Lookout, on North Carolina's Outer Banks, with winds of 85 mph (137 km/h), but exhibited an unusually low pressure of 951 mbar, which is typically found in a category 3 hurricane. After having tracked over land for about 10 hours, the eye of Irene became cloud-filled, although the center remained well-defined on radar images. Early in the evening of August 27, Irene re-emerged into the Atlantic near the southern end of the Chesapeake Bay in Virginia as a marginal Category 1 hurricane, slowly weakening as it continued northward and weakening to a tropical storm early on August 28. Shortly before sunrise, at 5:35 am EDT (09:35 UTC) on August 28, Irene made a second landfall at Brigantine in southeastern New Jersey near Atlantic City with winds of 70 mph (110 km/h) and soon after moved over water again, hugging the New Jersey coastline. About 3+1⁄2 hours later, Tropical Storm Irene made landfall with 65 mph (105 km/h) winds in the Coney Island neighborhood of Brooklyn, New York.^{[citation needed]}

Following its final New York landfall, Irene moved northeast over New England while maintaining its strength, before it was declared an extratropical cyclone early on August 29, while its center was located near the New Hampshire/Vermont border. During that day, the system continued to move towards the northeast, before it was absorbed by a frontal system early on August 30. This system, which the Free University of Berlin dubbed as Ex-Irene, continued moving northeastward for another few days, reaching Iceland on September 2. Afterward, the system stalled just south of Iceland and gradually weakened, before it was absorbed by another approaching extratropical cyclone to the west on September 6.