Typhoon Dujuan turns toward Kanto as Japan starts a five-day holiday

Typhoon Dujuan, Japan’s Typhoon No. 25, passed near the Ogasawara Islands on Saturday morning and continued west-northwest. The Japan Meteorological Agency said that at noon the centre sat about 270 kilometres west of Chichijima, with a central pressure of 975 hectopascals and maximum winds near the core of 30 metres per second, about 108 kilometres an hour. Chichijima had already recorded an instantaneous gust of 30.4 metres per second.

The agency’s working forecast on Saturday pointed to a stronger storm as it approaches the Izu Islands and the Kanto region around Monday night: pressure near 960 hectopascals, core winds around 35 metres per second, instantaneous gusts up to 50 metres per second over water and 35 on land. One track keeps a possible landfall on the Boso Peninsula in Chiba, east of Tokyo, on 21 September, two days into a five-day holiday.

NASA’s Aqua satellite had photographed the system over the Philippine Sea on 18 September. The Joint Typhoon Warning Center at 2100 UTC that day put Dujuan about 1,015 kilometres south of Yokosuka with sustained winds near 121 kilometres an hour, a Category 1 equivalent, and significant wave heights around 8.5 metres. By Saturday afternoon JMA described a storm still moving northwest at about 15 kilometres an hour south of Honshu, with gusts to 162 kilometres an hour in the broader field.

Rain totals in the 24 hours to noon on 20 September are forecast at 150 millimetres in the Izu Islands and the Kanto-Koshin region, which includes Tokyo, and 60 millimetres in Tohoku and Tokai. The hazard list is the standard one for a Kanto approach: high waves, landslides, swollen rivers, flooding in low wards. JR East said some services in Chiba and neighbouring prefectures may stop from late 20 September through 21 September.

Holiday timing is the part that turns a weather bulletin into a logistics problem. Families move. Trains fill. Coastal hotels sit in the gust field. A suspension order on the Sobu or Uchibo lines during a holiday Monday is a different event from the same order on a working Tuesday. Local governments in Chiba and the Izu chain have the usual checklist: evacuate flood-prone districts early, keep people off breakwaters, treat the first landslide warning as real.

Model guidance is not unanimous on landfall. Some runs send Dujuan around the ridge and keep the core southeast of the main island, with rain and wind still reaching eastern Honshu. JTWC discussion on Saturday described a track along the southwestern edge of a subtropical ridge, a turn northeast in about a day, and extratropical transition in three to four days. Intensity in that discussion holds near 120 kilometres an hour for two days, with a chance of a brief rise over the Kuroshio before shear increases.

For Tokyo the useful question is narrower than landfall. Even a bypassing storm at 960 hectopascals can close piers, delay Haneda and Narita banks, and knock trees onto suburban lines. Monday night to Tuesday morning is the window JMA is asking people to plan around. The holiday does not move. The typhoon might.