Photo/Illutration(The Asahi Shimbun)

Since the Japan Meteorological Agency began compiling records in 1951, Typhoon No. 12 stands out as the only one that has barreled across the Japanese archipelago from east to west.

The powerful typhoon took the rare path mainly because of the presence of a cold low-pressure system.

The occurrence of that low-pressure system is not rare in itself. However, influenced by the presence of two high-pressure systems, the typhoon took the rare path.

Typhoon No. 12, which formed south of Japan on July 25, moved northward along the Pacific high-pressure system. After that, it approached a cold low-pressure system, which was initially located east of Japan.

The cold low-pressure system slowly moved westward while maintaining a counterclockwise air flow. Then, the typhoon moved northwestward and then westward as if it was engulfed in the air flow of the cold low-pressure system.

Initially, it had been forecast for the typhoon to head northward and go into the Sea of Japan. However, a Tibetan high-pressure system spread to wider areas southward from the continent than had been anticipated. As a result, the typhoon was blocked by the Tibetan high-pressure system and moved westward.

As the typhoon is making a counterclockwise whirl, southerly winds enter the east side of the typhoon. As a result, air in the southern sea, which contains much moisture, collides with cold air on the north side of the typhoon, making atmospheric conditions unstable.

Conventional typhoons usually travel east. In the case of Typhoon No. 12, however, its eastern side is an area where it has already passed.

Therefore, the JMA cautioned, “Even after the typhoon has passed, strong winds or heavy rains could take place (due to the unstable atmospheric conditions).”