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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. ==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 reached a "high" probability of 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 located about 715 mi (1150 km) east of the Leeward Islands, moving westward to the south of a large ridge. Conditions were generally favorable for further intensification, with the exception of northeasterly wind shear. Late on August 21, a Hurricane Hunters mission observed flight-level winds of 51 mph (84 km/h), and on this basis the NHC upgraded the depression to Tropical Storm Isaac. Despite its intensification, the storm was disorganized with its center located 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 southwestern 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 was unable to 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 hurricane status about 75 mi (115 km) 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 80 mph (130 km/h). 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.〔(【引用サイトリンク】title=WPC's Advisories for Tropical Depression ISAAC )〕 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hurricane Isaac (2012)」の詳細全文を読む スポンサード リンク
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