The strong storm Tuesday that left four people dead and disrupted transportation systems nationwide was triggered by a case of rare weather conditions occurring simultaneously.

"This was a condition which is referred to as a 'May Storm,' " Maki Wakahara, a spokeswoman for the Japan Weather Association, told The Japan Times. "But it is extremely rare that it causes such huge damage."

The stormy weather halted bullet trains and grounded airplanes across the country. A maximum instantaneous wind velocity hit a record 143.3 kph in Tonami, Toyama Prefecture, where gusts flipped over trucks and knocked out power for 2,800 households, according to Hokuriku Electric Power Co.