Chiba’s Koitogawa River Floods as Typhoon Dujuan Hits Japan on September 21

Typhoon Dujuan triggered Japan’s highest flood alert for the Koitogawa River in Kimitsu, Chiba Prefecture on September 21, forcing emergency evacuation orders for 668 people in 299 households. The storm, the 25th typhoon of 2026, brought sustained winds of 143 kilometers per hour and rainfall that broke records across multiple cities. Nearly 1.9 million people received evacuation advisories nationwide as the typhoon tracked along Japan’s eastern coast during Silver Week holidays.

Level 5 alert issued for Koitogawa River flooding

The Kimitsu city government issued a Level 5 emergency alert, the highest on Japan’s disaster scale, for the Koitogawa River on September 21. This alert, labeled “緊急安全確保” (ensure safety immediately), warned of life-threatening flooding in the inundation zone. The alert covered 299 households with an estimated 668 residents in the flood-prone area near the river.

Typhoon Dujuan brings record rainfall and widespread damage

Typhoon Dujuan packed maximum sustained winds of 143 kilometers per hour with gusts reaching 198 kilometers per hour as it lingered offshore. Rainfall totals through September 22 were forecast to exceed average September monthly rainfall, creating record-breaking conditions. One person in Miyazaki Prefecture died, and over 50,000 households lost power across affected regions.

Evacuation orders and disruptions across eastern Japan

Nearly 1.9 million people received evacuation advisories as the typhoon approached the Tokyo metropolitan area on September 21. The Japan Meteorological Agency warned that linear rain bands could form over central Japan and the Kanto region, raising the risk of flash floods and landslides. Close to 400 flights were cancelled, and the Tokyo Game Show shut down ahead of its final day as the storm disrupted Silver Week holidays.

What residents should do now

The Japan Meteorological Agency urged residents in affected areas to check local disaster risk levels and follow municipal evacuation guidance. People in urban areas were advised to avoid flooded roads and underground facilities where water could accumulate. As of September 21 evening, wind speeds had dropped and alert levels were being downgraded, but heavy rain was still expected through September 22.

Final Thoughts

The Koitogawa River flooding marks one of the most serious impacts from Typhoon Dujuan in Chiba Prefecture. Residents in the 299 affected households should follow evacuation orders immediately and monitor local government updates for all-clear signals.

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