Typhoon Dujuan aims at Japan's Silver Week holiday and the Tokyo coast

Typhoon Dujuan, the 25th named storm of Japan's year, was 170 kilometres south-southeast of Chichijima in the Ogasawara Islands at 3 p.m. on Friday, 18 September. The Japan Meteorological Agency measured a central pressure of 975 hectopascals, sustained winds of 30 metres per second (108 kilometres per hour) and gusts to 45 metres per second (162 kilometres per hour). The system was moving west-northwest at 35 kilometres per hour and was classed as large.

The agency's afternoon bulletin put the centre near 25.6 degrees north, 142.7 degrees east. Winds of 50 knots or more extended 110 kilometres from the eye. Winds of 30 knots reached 750 kilometres to the northeast and 390 kilometres to the southwest. Forecast points take the storm west of the Ogasawara chain overnight, toward 27.2 degrees north, 139.3 degrees east by 3 p.m. Saturday, then north toward 30.7 degrees north, 138.2 degrees east by Sunday afternoon as it draws level with the Izu Islands.

Rain totals and the holiday calendar

Ogasawara was told to expect up to 250 millimetres in the 24 hours through noon Saturday. The Izu Islands could see 200 millimetres in the next window. For the 24 hours to 6 p.m. Monday, JMA numbers circulating through Jiji and local briefings put Tokai as high as 300 millimetres, with Kanto, the Pacific side of Tohoku and the Izu Islands around 200 millimetres. Forecaster Yoshikazu Yano noted thick cloud north of the centre. That cloud can drop rain before the eye arrives and push catchment totals above the single-day figures.

Silver Week runs through Wednesday. The holiday stack is the reason the storm is more than a marine warning. Families move between Tokyo and the provinces. Trains, expressways and domestic flights fill. Yano told the public to treat leisure and homecoming plans as flexible. The agency warned of landslides, flooding in low ground, high waves and transport delays across Kanto, Tokai, the Izu chain and the Pacific Tohoku coast.

Current thinking at JMA is that Dujuan will slide off toward waters east of Tohoku from Monday night and become an extratropical cyclone by Tuesday afternoon. That track would spare Tokyo a direct landfall and still soak the capital region. The difference between a near miss and a hit is measured in where the rain band sits, not in whether commuters get a dry Monday.

What to watch through the weekend

Three updates will tell the story. First, whether the centre stays west of the Izu chain or hooks closer to the mainland. Second, whether the northern rain shield stalls over the Tone and Fuji catchments. Third, whether rail operators pre-emptively cut services on Sunday night. JR East and the expressway companies usually decide late, once the 3 p.m. Sunday package is in.

Dujuan is not the strongest storm of the season. It is well timed. A large, wet system moving up the Pacific coast during a five-day break does its damage through cancelled trains and saturated slopes rather than through a single catastrophic landfall. People on Chichijima are already in the first rain. People in Tokyo still have a day to change their tickets. That gap is the only planning window the calendar has left.