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Hurricane Bertha was an unusual tropical cyclone in early August 2014 that attained minimal hurricane status, despite having a disheveled appearance and a relatively high atmospheric pressure. On July 26, a tropical wave south of the Cape Verde Islands was monitored for possible tropical cyclogenesis. Over the following days, it slowly developed and acquired gale-force winds and enough convection to be designated as ''Tropical Storm Bertha'' early on August 1. A mostly disorganized cyclone, Bertha quickly moved across the Lesser Antilles, clipping the northern end of Martinique, later that day. During its trek across the eastern Caribbean Sea, its circulation became severely disrupted and it may have degenerated into a tropical wave. On August 3, it traversed the Mona Passage and moved over the Southeastern Bahamas where conditions favored development. Despite an overall ragged appearance on satellite imagery, data from Hurricane Hunters indicated it intensified to a hurricane on August 4; it acquired peak winds of 80 mph (130 km/h) that day. Turning north, and later northeast, Bertha soon weakened as it began to merge with an approaching trough to the west. This merger ultimately took place on August 6, at which time Bertha was declared extratropical well to the south of Nova Scotia. The remnant system raced eastward across the Atlantic and later struck the United Kingdom on August 10. Once over the North Sea, the storm stalled for a few days before resuming its eastward track. It was last noted around the Baltic Sea on August 16. As a tropical cyclone, Bertha's impact was relatively minor. Widespread power outages occurred along its path but no major damage or loss of life took place. Enhanced swells and rip currents associated with the hurricane resulted in three fatalities and dozens of rescues along the East Coast of the United States. After becoming an extratropical system, it had significant effects in Western Europe. Particularly hard hit was the United Kingdom, where wind gusts reached . Unseasonably heavy rains triggered widespread flooding which shut down roads and prompted evacuations. One fatality took place offshore. On mainland Europe, a small tornado outbreak resulted in scattered structural damage in Belgium, France, and Germany. ==Meteorological history== On July 24, 2014, a westward moving tropical wave emerged off the west coast of Africa near the Cape Verde Islands. Following the development of convective activity —showers and thunderstorms— on July 26, National Hurricane Center (NHC) began monitoring the system for potential tropical cyclogenesis. A disorganized system, development was forecast to be slow due to unfavorable environmental conditions. Organization and coverage of convection began improving by July 28, due in part to the passage of a Kelvin wave.〔 An area of low pressure subsequently consolidated within the disturbance on July 29 and the NHC assessed the system as having imminent potential of becoming a tropical depression. Convection soon diminished over the system, though its circulation remained well-defined. Moving west-northwest around the periphery of a strong subtropical ridge,〔 the low acquired tropical storm-force winds early on July 31 but continued to lack convection. A hurricane hunter aircraft investigated the system that afternoon and found winds of 45 mph (75 km/h) north and northeast of the center. In the hours following the weather reconnaissance mission, a band of deep convection blossomed near the center, prompting the NHC to designate the system as ''Tropical Storm Bertha'' at 00:00 UTC on August 1. Upon its classification, Bertha was situated roughly east-southeast of Barbados in the Lesser Antilles.〔 Within hours of Bertha's designation on August 1, wind shear stemming from a trough over the central Atlantic displaced convection from the circulation center.〔 Satellite imagery depicted a well-defined and vigorous circulation; however, observations from the hurricane hunters indicated a wind field more akin to a tropical wave. Around 21:00 UTC, Bertha clipped the northern end of Martinique with sustained winds of 50 mph (85 km/h). Persistent shear continued to take its toll on the cyclone as it entered the Caribbean Sea with aircraft data indicating no closed circulation at elevation. Despite this, observations from Martinique and Dominica indicated that there was some semblance of a surface circulation, and the NHC continued to monitor Bertha as a tropical storm. Throughout August 2, convection steadily increased in coverage and organization though the center of Bertha remained displaced from the strongest thunderstorms to the southwest. NEXRAD weather radar imagery from San Juan, Puerto Rico depicted a disorganized, possibly open circulation throughout the day. In light of this, NHC forecaster John Beven noted that the system could degenerate into an open wave around the time in reached Hispaniola later on August 2. Continued effects of dry air entrainment, shear, and land interaction further degraded Bertha's structure and late on August 2, "the system barely () as a tropical cyclone".〔 Various data sources indicated no closed circulation by 21:00 UTC and it was noted that advisories could be discontinued, at least temporarily. Early on August 3, the disheveled storm moved through the Mona Passage and brushed the eastern coast of the Dominican Republic before emerging over the Atlantic Ocean. As the storm moved away from Hispaniola its movement became more northwesterly, following the edge of the subtropical ridge. Moving near the Turks and Caicos Islands, Bertha's circulation finally became better organized and banding features developing over its eastern periphery. Subsequent strengthening of upper-level outflow, decreased shear, increased mid-level humidity, and high sea surface temperatures enabled rapid intensification.〔 Deep convection wrapped cyclonically into the storm and winds reached 65 mph (100 km/h) by 03:00 UTC on August 4. During the early part of August 4, structural organization began to degrade with convection becoming more limited in extent and banding features dissipating. The only factor aiding the storm was its well-defined outflow. However, despite the storm's ragged and weak appearance observations from hurricane hunters indicated that it had intensified into a hurricane by 12:00 UTC.〔〔 Bertha is estimated to have reached its peak intensity around this time with winds of 80 mph (130 km/h) and a barometric pressure of 998 mbar (hPa; 29.47 inHg).〔 Additionally, by this time its movement had shifted to due north and with increased forward momentum. Through the remainder of August 4 and into the early hours of August 5, Bertha maintained hurricane status with its atypical structure. At times, its circulation became exposed due to increasing shear. Acceleration to the north-northeast ahead of a trough off the East Coast of the United States ensued as the system weakened below hurricane intensity during the overnight of August 4–5. Steadily increasing shear kept the circulation center mostly devoid of thunderstorms, with periodic bursts of convection being quickly pushed away. The storm's motion became more northeasterly early on August 6 as it began to undergo an extratropical transition. An upper-level jet streak coupled with the system that morning, prompting convection to develop away from the storm's center. Bertha soon merged with the trough steering it northeast as it moved into the cold sector of the front, which extended from Nova Scotia to The Bahamas. The merger of these systems marked Bertha's transition into an extratropical system, at which time it was located south-southeast of Halifax, Nova Scotia.〔 Slight intensification took place shortly thereafter with winds increasing to 60 mph (95 km/h) before weakening resumed. The system raced eastward across the Atlantic and ultimately degraded into a trough several hundred miles southwest of Ireland on August 9.〔 Bertha's remnants struck the United Kingdom the following day and later moved over the North Sea. There, the storm stalled for a few days before resuming its eastward track. The decaying cyclone moved over Scandinavia on August 14 and was last noted on August 16 near the Baltic Sea. 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 Bertha (2014)」の詳細全文を読む スポンサード リンク
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