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The 1991 Atlantic hurricane season was the first season in over 24 years in which no hurricanes developed from tropical waves, which are the source for most North Atlantic tropical cyclones. The hurricane season officially began on June 1, and ended on November 30. It was the least active in four years due to higher than usual wind shear across the Atlantic Ocean. The first storm, Ana, developed on July 2 off the southeast United States and dissipated without causing significant effects. Two other tropical storms in the season – Danny and Erika – did not significantly affect land. Danny dissipated east of the Lesser Antilles, and Erika passed through the Azores before becoming extratropical. In addition, there were four non-developing tropical depressions. The second depression of the season struck Mexico with significant accompanying rains. The most significant storm of the season was Hurricane Bob, which at the time was among the ten costliest United States hurricanes. After brushing the Outer Banks of North Carolina and Long Island in New York, the hurricane made landfall on Rhode Island. It caused $1.5 billion in damage (1991 USD), mostly in Massachusetts, and 17 fatalities. The strongest hurricane of the season was Claudette, which reached peak winds of 135 mph (215 km/h) near Bermuda. It passed near the island but did not cause any damage. Tropical Storm Fabian was the only tropical storm to move over or near Cuba or Florida, producing heavy rainfall but no damage. Hurricane Grace, the final named storm of the season, provided the energy that led to the development of a powerful nor'easter known as the Perfect Storm. Originating from an extratropical storm, the Perfect Storm intensified while moving westward toward New England, leaving $200 million in damage and causing coastal damage from Puerto Rico to Florida and northward through Canada. It later transitioned into a hurricane over the Gulf Stream, finally dissipating over Nova Scotia on November 2. Also Storms Blanca, Carlos, Delores, Enrique, Guillermo, Hilda, Ignacio, Jimena, Kevin, Linda and Marty(See The 1991 pacific hurricane season) had their origins in the atlantic but did not strengthen into a depression until they reached the eastern pacific. Also Tropical Storm Danny and Hurricane Jimena formed from the same tropical wave. ==Season summary== Before the start of the season, hurricane expert William M. Gray released his forecast for the year's activity, a yearly practice that he began in 1984. In early April, Gray anticipated a "mild" season with fewer than ten tropical storms, of which less than six would become hurricanes. Later that month, the Weather Research Center forecast ten named storms and six hurricanes, of which five would become major hurricanes while three would hit the United States. In early June, Gray released an updated report that predicted the formation of eight tropical storms, four hurricanes, and one major hurricane. The revised June total was very close to the actual season activity, with the exception of forecasting one fewer major hurricane.〔 However, a later revision in August incorrectly anticipated less activity, when Gray predicted seven storms and three hurricanes. Overall activity in 1991 was below normal. This was partially due to decreased tropical cyclogenesis from African tropical waves, which are troughs that move across the ocean with associated convection. In most seasons, the majority of storms develop from tropical waves. Of the season's twelve tropical cyclones, only five originated from tropical waves; in addition, only three of the eight tropical storms were from tropical waves, and none had the characteristics of a Cape Verde-type hurricane. From late April to late November, there were 73 tropical waves that exited the west coast of Africa. The total was higher than average, although many of them were poorly defined and had little thunderstorm activity. The waves traversed the Atlantic Ocean further south than normal, typically not becoming convectively active until moving across northern South America. Cyclogenesis was also suppressed by higher than normal wind shear, as well as low rainfall amounts across the Sahel.〔 There were also no tropical storms in the Gulf of Mexico for only the third time in the 20th century, after 1927 and 1962.〔 The season produced twelve tropical depressions, which was the lowest in five years. The eight tropical storms was the lowest amount in four years. Four of the storms developed into hurricanes, although for the first time in over 24 years none were from tropical waves.〔 The season's activity was reflected with a low cumulative accumulated cyclone energy (ACE) rating of 36. ACE is, broadly speaking, a measure of the power of the hurricane multiplied by the length of time it existed, so storms that last a long time, as well as particularly strong hurricanes, have high ACEs. ACE is only calculated for full advisories on tropical systems at or exceeding 34 knots (39 mph, 63 km/h) or tropical storm strength. Although officially, subtropical cyclones are excluded from the total, the figure above includes periods when storms were in a subtropical phase. 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「1991 Atlantic hurricane season」の詳細全文を読む スポンサード リンク
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