Typhoon No. 24 closed in on Okinawa Prefecture and the Amami region of Kagoshima Prefecture on September 3, The Yomiuri Shimbun reported on September 3. The storm is expected to move into the East China Sea by September 4 before turning south and lingering around Okinawa until roughly September 8.

The slow-moving system is set to combine with an autumn rain front stalled along the southern coast of Honshu, drawing warm, humid air northwards and raising the risk of sustained downpours across Japan through about September 7.

The Japan Meteorological Agency said violent rain was forecast for western Japan on September 4. In the 24 hours to 6pm that day, rainfall was projected to reach up to 300 millimetres in Shikoku, 200 millimetres in Kyushu and 180 millimetres in the Kinki region.

The agency issued a half-day-ahead advisory warning that linear rain bands, the narrow, stationary lines of thunderstorms that have caused deadly flooding and landslides in Japan in recent years, could form over Kochi, Miyazaki and Kagoshima prefectures through the night of September 4.

Rainfall in the Kanto-Koshin region, which includes Tokyo, was forecast to reach a maximum of 120 millimetres in the 24 hours to 6pm on September 5.

As of 9pm on September 3, Typhoon No. 24 was about 50 kilometres southwest of Amami City in Kagoshima Prefecture, moving north at 20 kilometres per hour. Its central pressure was 990 hectopascals, with maximum sustained winds near the centre of 20 metres per second.