A Statistical Study of Tornadoes and Waterspouts in Japan from 1961 to 1993

Abstract

A database on tornadoes and waterspouts in Japan from 1961 to 1993, which is believed to be most reliable at present, was compiled after an extensive survey of apparently almost all existing literature. Six hundred and seventy-seven tornadoes and 148 waterspouts were cataloged in the database, which is operated on a personal computer basis. Various statistical characteristics of tornadoes and waterspouts have been examined: 1) On average 20.5 tornadoes and 4.5 waterspouts occur per year in Japan. 2) Tornadoes occur most frequently in September and least frequently in March. Waterspouts occur most frequently in October. 3) Both tornadoes and waterspouts have high activities during daytime. The activity of tornadoes has two peaks between 1000 and 1100, and between 1500 and 1600 JST (Japan Standard Time). 4) About two-fifths of the tornadoes occur on multiple-tornado days. 5) The average lifetimes of tornadoes and waterspouts are 12 and 14 min, respectively. 6) About 15% of tornadoes are anticyclonic. 7) More than 50% of tornadoes move toward the northeast quadrant. Their average speed is 10 m s?1. 8) The average damage path width and pathlength are 98 m and 3.2 km, respectively. 9) Fatality and injuries caused by tornadoes per year are 0.58 and 29.7, respectively. Completely destroyed, severely damaged, and partly damaged residential houses per year are 17.0, 39.0, and 329, respectively. 10) About 46% of tornadoes are associated with extratropical cyclones (16% in a warm sector and 15% associated with cold fronts) and 20% associated with typhoons. 11) A preliminary estimate of risk of a tornado encounter for each of 47 prefectures was made. The shortest recurrence interval is found for Tokyo Prefecture and is less than 7.7 ? 103 yr. The recurrence interval for the whole country of Japan is less than 1.7 ? 105 yr. A preliminary discussion on the stability of the tornado statistics was also made.