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The list of Category 5 Atlantic hurricanes encompasses 33 tropical cyclones that reached Category 5 strength on the Saffir–Simpson hurricane wind scale within the Atlantic Ocean (north of the equator), Caribbean Sea and Gulf of Mexico. Hurricanes of such intensity are somewhat infrequent in the Atlantic basin, occurring only once every three years on average. Only six times—in the 1932, 1933, 1960, 1961, 2005, and 2007 hurricane seasons—has more than one Category 5 hurricane formed. Only in 2005 have more than two Category 5 hurricanes formed, and only in 2007 has more than one made landfall at Category 5 strength. ==Statistics== A Category 5 hurricane has sustained winds greater than . "Sustained winds" refers to the average wind speed observed over one minute at above ground, which is the standard height windspeed is measured at to avoid interference by obstacles and obstructions. Brief gusts in hurricanes are typically up to 50 percent higher than sustained winds. Because a hurricane is (usually) a moving system, the wind field is asymmetric, with the strongest winds on the right side (in the Northern Hemisphere), relative to the direction of motion. The highest winds given in advisories are those from the right side. Between 1924 and 2007, 33 hurricanes were recorded at Category 5 strength. No Category 5 hurricanes were observed officially before 1924. It can be presumed that earlier storms reached Category 5 strength over open waters, but the strongest winds were not measured. The anemometer, a device used for measuring wind speed, was invented in 1846. However, during major hurricane strikes the instruments as a whole were often blown away, leaving the hurricane′s peak intensity unrecorded. For example, as the Great Beaufort Hurricane of 1879 struck North Carolina, the anemometer cups were blown away when indicating . A reanalysis of weather data is ongoing by researchers who may upgrade or downgrade other Atlantic hurricanes currently listed at Categories 4 and 5. For example, the 1825 Santa Ana hurricane is suspected to have reached Category 5 strength. Furthermore, paleotempestological research aims to identify past major hurricanes by comparing sedimentary evidence of recent and past hurricane strikes. For example, a “giant hurricane” significantly more powerful than Hurricane Hattie (Category 5) has been identified in Belizean sediment, having struck the region sometime before 1500. Officially, the decade with the most Category 5 hurricanes is 2000–2009, with eight Category 5 hurricanes having occurred: Isabel (2003), Ivan (2004), Emily (2005), Katrina (2005), Rita (2005), Wilma (2005), Dean (2007), and Felix (2007). The previous decades with the most Category 5 hurricanes were the 1930s and 1960s, with six occurring between 1930 and 1939 (before naming began) and again between 1960 and 1969. (Ethel, Donna, Carla, Hattie, Beulah, and Camille).〔 Seven Atlantic hurricanes—Camille, Allen, Andrew, Isabel, Ivan, Dean and Felix—reached Category 5 intensity on more than one occasion; that is, by reaching Category 5 intensity, weakening to a Category 4 or lower, and then becoming a Category 5 again. Such hurricanes have their dates shown together. Camille, Andrew, Dean and Felix each attained Category 5 status twice during their lifespans. Allen, Isabel and Ivan reached Category 5 intensity on three separate occasions. However, no Atlantic hurricane has reached Category 5 intensity more than three times during its lifespan. The November 1932 Cuba hurricane holds the record for most time spent as a Category 5 (although it took place before satellite or reconnaissance so the record may be somewhat suspect).〔 The minimum pressure of the more recent systems was measured by recon aircraft using dropsondes, or by determining it from satellite imagery using the Dvorak technique. For older storms, pressures are often incomplete. The only readings came from ship reports, land observations, or aircraft reconnaissance. None of these methods can provide constant pressure measurements. Thus, sometimes the only measurement can be from when the hurricane was not a Category 5. Consequently, the lowest measurement is sometimes unrealistically high for a Category 5 hurricane. For example, the 1938 New England hurricane had its lowest recorded pressure recorded while it was a Category 3 storm. These pressure values do not match up with the wind readings. This happens because the wind speed of a hurricane depends on both its size and how rapidly the pressure drops as the hurricane's center approaches. Thus, a hurricane in an environment of high ambient pressure will have stronger winds than a hurricane in an environment of low ambient pressure, even if they have identical central pressures. 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「List of Category 5 Atlantic hurricanes」の詳細全文を読む スポンサード リンク
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