Photo/IllutrationA railroad bridge for the JR Suigun Line over the Kujigawa river is seen collapsed in Daigo, Ibaraki Prefecture, on Oct. 13. (Shigenori Komatsu)

  • Photo/Illustraion
  • Photo/Illustraion

Monstrous Typhoon No. 19 was the creation of a "perfect storm," maintaining its massive strength due to a convergence of meteorological conditions, weather officials said.

The powerful storm left behind a wide-reaching impact on the Japanese archipelago, and forced the Japan Meteorological Agency to issue its highest emergency Level 5 rain warning in Tokyo and 12 prefectures.

In these areas, active rain clouds had been observed off and on before the typhoon made landfall on the evening of Oct. 12 in the Izu Peninsula in Shizuoka Prefecture.

The massive typhoon dumped heavy rain scattered over a wide sphere for long hours, resulting in record rainfall totals in many locales.

“Widely developed rain clouds lie to the north side of the center of the typhoon, which caused record rainfalls,” Yasushi Kajihara, who heads the agency’s forecast division, said during a news conference on the afternoon of Oct. 12, about the characteristics of Typhoon No. 19.

As the typhoon approached and made landfall, warm and humid winds blown in from the east and southeast hit the mountains in Chichibu and Tanzawa of the Kanto region, the Izu Peninsula in Shizuoka Prefecture and southern parts of the Tohoku region. Such movements created strong updrafts, resulting in rain clouds one after another on a broad scale.

Weather experts say that one of the primary reasons for such a record amount of rain is that the typhoon maintained a massive scale and extremely powerful strength while approaching the main island of Japan.

Kazuhisa Tsuboki, a professor of meteorology at Nagoya University, said the sequencing of Typhoon No. 19 from its formation through development to approach “took an astonishing course.”

Immediately after the typhoon was formed, its central pressure dropped rapidly in one day. An extremely big chunk of clouds then appeared due to meteorological conditions such as sea water temperatures and atmospheric convection.

Tsuboki said such an initial formation phase of Typhoon No. 19 significantly differed from that of Typhoon No. 15, which was compact in size but caused major damage in Chiba Prefecture in September.

Typhoon No. 19 moved to the north afterward, but its central pressure remained low while maintaining strength.

The sea water temperature in the area immediately south of Japan was more than 27 degrees, one to two degrees higher than in an average year. Because of that, the typhoon absorbed lots of moisture--its source of energy.

“In October, normally dry winds from the northwest enter (the area) and take moisture from a typhoon, so that the density of clouds decreases as the typhoon draws closer to Japan,” Tsuboki said. “This time, however, the typhoon got to Japan with strong rain clouds intact.”

Because Typhoon No. 19 was so widespread and powerful as its strong wind area covered more than half of Japan's mainland, it was accompanied by various weather-related phenomenon, such as violent winds and high tides, as well as heavy rains.

The agency said the Pacific high-pressure system was extending out more than an average year when the typhoon approached Japan. The typhoon moved northward as it circled the edges of the system.

Then it changed course to the east, due to westerly winds. Such moves made the typhoon hit the Kanto region directly.

(This article was written by Norihiko Kuwabara and Maiko Kobayashi.)