Cleanup begins after Kanto tornado

Supercell may have been cause of twister, weather officials say

Kyodo

Recovery and repair efforts continued Tuesday, a day after a tornado tore a path through Koshigaya, Saitama Prefecture, and Noda, Chiba Prefecture.

Meanwhile, the Meteorological Agency continued its investigation into whether the tornado was produced by a supercell, the least common type of thunderstorm but capable of producing severe weather, including tornadoes.

Tornadoes form due to a twisting motion of rising air, the columns of which are in contact with dense cumulonimbus clouds. The rapid decreasing air pressure at the tornado center triggers extremely strong winds.

According to data taken at the upper stratosphere over Tsukuba, Ibaraki Prefecture, the temperature at about 6,000 meters above the ground was not unusual at around 9 a.m. Monday. At about 1,500 meters, however, the temperature reached 19 degrees, 2 degrees above normal. The rise in temperature was triggered by southerly winds generated by Pacific subtropical anticyclones.

The forecast was for sunny weather with a high of 34 degrees in Koshigaya, which was 3.5 degrees higher than usual.

Local weather fronts that did not appear on weather charts are also believed to have contributed to the creation of the tornado. A collision of two air masses from north and south due to winds high above western Tokyo to Saitama and Ibaraki prefectures caused a large temperature difference in a widespread area. Updrafts generated by the confrontation of air masses produced cumulonimbus clouds.

Radar stations also detected a mesocyclone, a counterclockwise vertical rotation often associated with updrafts in supercells, which caused the cumulonimbus clouds to move from southern Saitama Prefecture toward the northeast.

Early Monday, the Meteorological Agency issued an alert that strong gusts or tornadoes were likely to occur through the evening in the Kanto-Koshin region. Tornado warnings for Saitama and Chiba prefectures were issued at 2:11 p.m., soon after a strong gust developed in the city of Koshigaya.

The agency’s Meteorological Research Institute speculates that if global warming progresses, weather conditions in Japan will become more favorable for the formation of tornadoes.

“We should be prepared for more tornadoes connected to global warming,” said Masahide Kimoto, vice director and a professor at the Atmosphere and Ocean Research Institute of the University of Tokyo.

A supercell was also the cause of a deadly tornado that struck Tsukuba, Ibaraki Prefecture, in May 2012.

Meanwhile on Tuesday, people whose houses were destroyed or damaged by the tornado began cleaning up.

“A carpenter covered my house with a blue tarp, but I can’t stay here,” said Mie Takamatsu, 63, whose house in the Osugi neighborhood in Koshigaya was hit by the tornado.

“It will cost me several million yen to repair it and I don’t feel financially secure,” Takamatsu said.

She said she sought shelter in the home of an acquaintance after the tornado ripped the roof off her house.

City workers in Koshigaya gathered up wreckage from destroyed houses and placed the debris in nine different parks.

According to Saitama and Chiba police, the tornado struck between 2:05 p.m. and 2:30 p.m., tearing a 13.8-km path from Iwatsuki Ward in the city of Saitama, through Koshigaya and Matsubushi, Saitama Prefecture, and on to Noda, Chiba Prefecture.

The tornado, which left 67 people injured and more than 540 household damaged or destroyed, also toppled electricity lines, knocking out power to numerous homes.

According to Tokyo Electric Power Co., the power outage continued until around 7:40 a.m. Tuesday for 785 households in Koshigaya.