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Arizona has been affected by hurricanes on numerous occasions. Usually, these storms originate in the eastern Pacific Ocean, make landfall in the Mexican states of Baja California or Sonora, and dissipate before crossing into the United States. Thus, in most cases, it is only the tropical cyclones' remnant moisture that produces heavy rainfall—and in some occasions, flooding—in portions of Arizona. However, approximately every five years, a tropical cyclone retains sufficient strength to enter the state as a tropical storm or a tropical depression. Arizonans can expect indirect flash floods caused by the remnants of tropical cyclones to occur about every two years.〔 Tropical cyclones in Arizona are not common, since the predominant wind pattern steers most storms that form in the Eastern Pacific either parallel or away from the Pacific coast of northwestern Mexico. As a result, most storms that could affect Arizona are carried away from the United States, with only 6% of all Pacific hurricanes entering US territory. Not all Arizona hurricanes originate from the Pacific Ocean, however; in July 2008 an Atlantic hurricane named Hurricane Dolly produced rainfall in the eastern portion of the state, and another Atlantic storm reached Arizona as a tropical depression. Many, but not all, of these systems also impacted California. Despite their rarity, hurricanes are among Arizona's most significant weather makers. In years when Arizona is affected by a tropical cyclone, these can be responsible for up to 25% of the rainfall in areas along the Colorado River. Arizona hurricanes are also responsible for torrential rains in localized areas, with the state's 24-hour rainfall record— of precipitation〔—occurring during Hurricane Nora's landfall in 1997. The heavy rainfall can trigger extensive flash floods, such as the ones produced by the remnants of Tropical Storm Octave in 1983, or the lingering moisture from Tropical Storm Emilia in 2006. ==Climatology== Tropical cyclones are not common over Arizona, but on average, a tropical storm or a tropical depression enters the state approximately every five years. However, indirect flash floods caused by the remnants of tropical cyclones are more common, as they tend to occur about every two years.〔(【引用サイトリンク】title=Tropical cyclones in Arizona )〕 Storms that approach the southwestern United States, and by extension Arizona, generally form closer to the Mexican shoreline than average, making them more likely to recurve northwards under the influence of an approaching trough. These troughs tend to extend farther to the south during the latter part of the Pacific hurricane season, in the period between late August and early October. These pronounced troughs thus produce a synoptic-scale flow that is conducive to steering hurricanes towards the southwestern United States. The infusions of tropical moisture from Arizona-bound tropical cyclones can be a significant portion of the rainfall in the region. In years when hurricanes approach Arizona, eastern and northern portions of the state receive on average 6–8% of the monsoon-season precipitation from tropical systems and their remnants. This percentage rises towards the southwestern corner of the state, which can receive up to a quarter of its monsoon-season rainfall from tropical cyclones.〔 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 Arizona hurricanes」の詳細全文を読む スポンサード リンク
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