Hurricane Isaac was a deadly and destructive tropical cyclone that came ashore in 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 west coast of Africa on August 16. Tracking generally west, a broad area of low pressure developed along the wave axis the next day, and the disturbance developed into a tropical depression early on August 21 while several hundred miles east of the Lesser Antilles. The system intensified into a tropical storm shortly thereafter, but high wind shear initially prevented much change in strength.
Isaac tracked between Guadeloupe and Dominica late on August 22, and then turned towards the west-northwest and entered a region favorable for intensification; it passed over Haiti and Cuba at strong tropical storm strength. A ridge of high pressure to Isaac's north intensified and turned it westward over the Florida Keys by August 26, and Isaac entered the eastern Gulf of Mexico the next day. Gradual intensification occurred, in which the system reached its peak intensity as a Category 1 hurricane, with 1-minute sustained winds of , 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.
Before it became a hurricane, Isaac produced flooding rain 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. Gusty winds and rainfall were reported in Cuba, but damage was limited to a few buildings. In Florida, Isaac produced several inches of rain, 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 after the storm was upgraded to hurricane intensity.
Tropical storm-force sustained winds, with gusts well over hurricane strength, knocked out power to hundreds of thousands, and heavy rain led to flooding. Many dams along the coast were briefly over-topped, though they did not break completely and were later pumped to prevent failure. Gusts near hurricane intensity and heavy rain also led to widespread power outages in the neighboring state of Mississippi, and parts of Alabama recorded nearly of rain. As an extratropical cyclone, Isaac produced torrential rains across Arkansas, flooding numerous streets and homes, and damaging many crops across the region. Strong winds felled downed lines and trees. Overall, Isaac caused $3.84 billion (2012 USD) in damage and led to 41 fatalities.
Meteorological history
A tropical wave crossed the west coast of Africa between August 15 and August 16. Later that day and early on August 17, the system began developing more convection, while located just west of Sierra Leone. As a result, the National Hurricane Center (NHC) began monitoring the system in the Tropical Weather Outlooks (TWOs). Thereafter, further organization briefly halted, though by early on August 18, associated convection became more concentrated. On the following day, the wave had a "high" probability of undergoing tropical cyclogenesis. Between early on August 19 and early on August 21, minimal structural improvement occurred, despite increases in development probability. By August 21, the system developed enough organization for the NHC to initiate advisories on Tropical Depression Nine; at the time, the depression was about east of the Leeward Islands, moving west to the south of a large ridge. Conditions were generally favorable for further intensification, except for northeasterly wind shear.
Late on August 21, a Hurricane Hunters mission observed flight-level winds of , and on this basis the NHC upgraded the depression to Tropical Storm Isaac. Despite its intensification, the storm was disorganized with its center north of the deepest convection. The circulation became elongated early on August 22, and the storm absorbed drier air in its northeast quadrant. Later that day, the low pressure area passed just south of Guadeloupe and into the Caribbean Sea. Dry air continued to hinder convection, although Isaac gradually became better organized. By late on August 24, the Hurricane Hunters observed a well-defined circulation; by that time, however, the strongest convection was moving over Hispaniola. An eye feature developed early on August 25, and Isaac attained winds of before crossing the southwest peninsula of Haiti.
While moving across Haiti, the circulation of Isaac became disrupted while the convection became disorganized. Continuing to the northwest, the storm moved along the north coast of Cuba. Convection increased over the center by early on August 26, and Isaac re-intensified slightly while entering the Straits of Florida. However, continued dry air prevented the inner core of convection from developing. Hurricane Hunters reported that a ragged eye developed multiple times, but the feature did not persist. The storm tracked northwestward across the Gulf of Mexico due to a subtropical ridge to its north. Although the barometric pressure continued to decrease, Isaac remained a large storm, which contributed to the lack of strengthening. At about 1620 UTC (11:20 a.m. CDT) on August 28, Isaac attained Category 1 hurricane status about south-southeast of the mouth of the Mississippi River, based on data from the Hurricane Hunters.
After further intensification, Isaac made landfall at 2345 UTC (6:45 p.m. CDT) on August 28, just southwest of the mouth of the Mississippi River with winds of . The eye moved back over water shortly thereafter, crawling just offshore of southeastern Louisiana (with little change in strength) before Isaac struck Louisiana again just west of Port Fourchon at 0715 UTC (2:15 a.m. CDT) on August 29. Hours after it made landfall, Isaac's eye became less circular and was open on the western side. Around 1900 UTC (2:00 p.m. CDT) on August 29, the hurricane weakened into a tropical storm as it slowly moved through Louisiana. Despite its weakening, Isaac continued to produce strong thunderstorms to the east and southwest of the center. Around 2100 UTC (4:00 p.m. CDT) on August 30, Isaac degenerated into a tropical depression over northern Louisiana. The Hydrometeorological Prediction Center took over the responsibility on issuing advisories from the NHC at 0300 UTC on August 31. The depression continued generally northeastward over Arkansas and Missouri before transitioning into an extratropical cyclone on September 1 as it interacted with an upper-level trough. The remnants of Isaac continued generally eastward over southern Illinois before moving southward over Kentucky. On September 3, the mid-level circulation of the storm split into two parts, with one portion continuing southward into the Gulf of Mexico and the other eastward over Ohio.
Preparations
Lesser Antilles
Upon the issuance of the National Hurricane Center's first advisory for Tropical Depression Nine early on August 21, numerous islands across the Lesser Antilles were placed under hurricane watches or tropical storm warnings. By the end of the day, tropical storm warnings were in place for was issued for Anguilla, Antigua, Barbuda, the British Virgin Islands, Culebra, Dominica, Guadeloupe, Desirade, Les Saintes, Marie Galante, Martinique, Montserrat, Nevis, Puerto Rico, Saba, St. Eustatius, St. Maarten, St. Martin, St. Kitts, United States Virgin Islands, and Vieques. Hurricanes watches were also in place for Puerto Rico, Vieques, Culebra, and the United States Virgin Islands. As the storm continued westward towards the region, a hurricane watch was issued for the British Virgin Islands on August 22. Later that day, Isaac entered the eastern Caribbean Sea as a minimal tropical storm rather than a hurricane, resulting in the discontinuation of all previously issued hurricane watches. As the storm gradually moved further westward into the Caribbean, warnings were discontinued for the various islands, with all warnings ceasing by the end of August 23.
Greater Antilles and The Bahamas At 0900 UTC on August 22, the government of the Dominican Republic issued a tropical storm watch along the north coast of the Dominican Republic, from the border with Haiti eastward to Saona Island. Simultaneously, a hurricane watch was put into place on the south coast, also extending from the Haitian border to Saona Island. At Guantanamo Bay Naval Base, a trial for five prisoners, who allegedly planned the September 11 attacks, was postponed.
At 1030 UTC on August 24, the government of Jamaica issued a tropical storm watch for the entire island of Jamaica. Early on the following day, the Cayman Islands Meteorological Service designated the Cayman Islands under a tropical storm watch. Several hours later on August 25, the tropical storm watches for both Jamaica and the Cayman Islands were discontinued.
Gulf of Mexico Oil production in the Gulf of Mexico was down by 24% percent and gas off by 8%, as several major companies (including BP and Shell) evacuated their installations in the east part of the basin. Overall, at least 39 (7%) of 596 production platforms and eight (11%) of 76 Gulf oil rigs were evacuated in the Gulf on August 26.Energy companies evacuate oil rigs, slash production, as Tropical Storm Isaac approaches Gulf Washington Post By the evening of August 27, approximately 78% of the Gulf's crude oil production and 48% of its natural gas production had been closed.
United States
Florida
At 2100 UTC on August 24, a tropical storm watch was issued for all of Florida south of the Jupiter Inlet on the east coast and south of Bonita Springs; it also included Lake Okeechobee and the Florida Keys. Early on the next day, the tropical storm watch was upgraded to a warning, while the Florida Keys and the mainland from Ocean Reef to Bonita Springs were now under a hurricane watch. Further north, a tropical storm watch was issued from the Jupiter Inlet to the Sebastian Inlet. Later on August 25, the hurricane watch was switched to a warning, while a separate hurricane watch was issued from Golden Beach southward.