The deadly tornadoes that struck the Kanto region last weekend have again shown the difficulties of predicting the phenomenon and the risk to the public.
Compared with the United States, which reportedly experiences around 800 twisters each year, forecasting them is harder domestically because their infrequency has prevented scientists from gathering sufficient data.
Disaster mitigation experts, meanwhile, say all the public can do is pay close attention to warning signs and stay indoors if a tornado hits their community.
A teenager died Sunday when a tornado tore through Tsukuba, Ibaraki Prefecture, after a warm air mass enveloped northern Kanto and raised temperatures in many locations.
According to the Meteorological Agency, the mercury rose to 25.8 degrees in Tsukuba, while a cold air mass of minus 19.1 degrees moved over the city at an altitude of about 5,500 meters at around 9 a.m.
This 45-degree variance may have caused a sharp updraft that generated supercell thunderstorms, one of the few cloud formations that can spawn tornadoes.
Ibaraki’s regional weather observatory in Mito issued the first tornado advisory at 12:38 p.m. Sunday, but the twister that ripped through Tsukuba and surrounding areas is thought to have been generated just seven minutes later.
“The advisory was issued for the entire prefecture and before we knew it, the damage had already been done,” said a municipal disaster management official. “We just didn’t have enough time to warn residents (in Tsukuba).”
The tornado, which cut a narrow swath through the area at around 70 kph, caught local residents and municipal officials completely off guard.
Predicting twisters involves monitoring mesocyclone vortexes, or whirlwinds several kilometers in diameter that form inside certain thunderstorms.
To this end, the Meteorological Agency has installed Doppler weather radars at 17 locations nationwide that record detailed raindrop movements and wind directions. The agency issues tornado advisories based on this data.
Hiroshi Niino, director of the Atmosphere and Ocean Research Institute at the University of Tokyo, said the United States employs a similar technique to minimize the annual death toll and destruction from tornadoes.
The major difference, however, is that Washington has set up a comprehensive nationwide radar network and also an information-sharing system involving tornado spotters and researchers to give weather forecasters a better chance of spotting twisters sooner, Niino said.
But despite such technological advances, twister forecasts are only accurate around 20 percent of the time even in the U.S.
“Before working out new ways to use what little information we have more effectively, everyone needs to realize that predicting such phenomena is an extremely complex task,” Niino stressed.
Domestic research institutes and businesses are already experimenting with new ways of improving the accuracy of such forecasts.
East Japan Railway Co. started implementing countermeasures against sudden wind blasts after a powerful gust overturned three cars of an express train in December 2005, killing five people and injuring 33 on the Uetsu Line in Yamagata Prefecture.
The railway has been analyzing data provided by the weather agency on cold fronts and cumulonimbus clouds — towering vertical clouds that can turn into supercells. JR East is using the results yielded to date on an experimental basis on the Uetsu and other lines between November and March.
Meanwhile, Kazuhisa Tsuboki, a meteorology professor at Nagoya University’s Hydrospheric Atmospheric Research Center, has developed a numerical model that generates computer simulations of tornadoes through data such as temperature, air pressure, humidity and wind velocity.
“But computer simulations don’t work fast enough yet, meaning it is still difficult for us to make twister predictions in time,” Tsuboki said.
In addition, scientists must overcome many other major hurdles before such simulations become a viable option.
In Japan, tornadoes are normally observed during the typhoon season from summer to autumn, with September considered the peak month. But the incident Sunday suggests similar thunderclouds may be able to form regardless of the season or location.
If that hypothesis is confirmed, what can the public do to protect itself against a sudden, unforeseen tornado?
“Paying close attention to climatic precursors increases the likelihood of avoiding a worst-case scenario,” said Yukio Tamura, a professor at Tokyo Polytechnic University specializing in wind blast mitigation measures.
In the Ibaraki city of Joso, near Tsukuba, many residents reported abnormal weather phenomena less than a minute before the tornado struck.
“The sunny sky suddenly turned dark, and it started hailing and thundering,” said Shiro Sakairi, head of a tea leaf processing factory in the area.
But if residents are caught unawares, their best bet of surviving is to take refuge indoors, Tamura said.
“You should stay indoors, away from windows and preferably in a toilet, bathroom or some other small confined space,” he said. “And if you can’t flee into a building, it’s better to shelter somewhere below ground level, such as a ditch.”