Hurricane Isaac was a deadly and destructive tropical cyclone that came ashore the U.S. state of Louisiana during August 2012. The ninth named storm and fourth hurricane of the annual hurricane season, Isaac originated from a tropical wave that moved off the western coast of Africa on August 16. Tracking generally west, a broad area of low pressure developed along the wave axis the following day, and the disturbance developed into a tropical depression early on August 21 while situated several hundred miles east of the Lesser Antilles. Though the system intensified into a tropical storm shortly thereafter, high wind shear initially prevented much change in strength.
After tracking between Guadeloupe and Dominica late on August 22, Isaac turned towards the west-northwest and entered a region favorable for intensification; it passed over Haiti and Cuba at moderate tropical storm strength. An intensification of the ridge of high pressure to the cyclone's north caused it to turn westward over the Florida Keys by August 26, and Isaac entered the eastern Gulf of Mexico the following day. Gradual intensification occurred, in which the system reached its peak intensity of 80 mph (130 km/h) prior to making two landfalls, both at the same intensity, on the coast of Louisiana during the late evening hours of August 28 and early morning hours of August 29, respectively. The system gradually weakened once inland, but still produced a widespread tornado outbreak across the middle of the country before dissipating into an open low early on September 1.
Prior to becoming a hurricane, Isaac produced flooding rainfall across much of the Lesser and Greater Antilles. Particularly hard hit was the island of Haiti, where 24 people lost their lives. Overflowing rivers led to significant structural damage and many roadways were washed away, preventing aid to the affected area. While gusty winds and rainfall were reported in Cuba, damage was limited to a few buildings. In Florida, Isaac produced several inches of rainfall, leading to flooding. Strong winds knocked out power to thousands, and waves along the coast caused minor beach erosion. The most severe effects of the storm, however, occurred in Louisiana following the storm's upgrade to hurricane intensity.
Tropical storm-force sustained winds, with gusts well over hurricane strength, knocked out power to hundreds of thousands, while heavy rainfall led to flooding. Many dams along the coastline were briefly over-topped, though they did not break completely and were later pumped to prevent failure. Gusts near hurricane intensity and heavy rainfall also led to widespread power outages in the neighboring state of Mississippi, while portions of Alabama recorded nearly 1 ft (0.3 m) of precipitation. As an extratropical cyclone, Isaac produced torrential rains across Arkansas, flooding numerous streets and homes, and damaging many crops across the region. Strong winds contributed to downed lines and trees. Overall, Isaac caused $2.39 billion (2012 USD) in damage and led to 41 fatalities.