After affecting Taiwan and China, Rammasun began weakening due to an approaching trough, which turned the typhoon northeastward.

After weakening to a tropical storm, Rammasun passed just west of the South Korean island of Jeju-do, killing one person from high waves.

The easternmost one eventually developed into Typhoon Chataan, and the western disturbance persisted to the east of Palau with an associated area of convection.

[1] Early on June 28, the Japan Meteorological Agency (JMA) [nb 2] classified the system as a tropical depression near Yap in the Federated States of Micronesia (FSM).

[1] That day, the JMA and the JTWC upgraded the storm to a typhoon about 930 km (580 mi) east of Luzon in the Philippines.

[1] While at peak intensity, Rammasun turned northward, steered around the subtropical ridge to its east,[1] and early on July 3 it struck the Japanese island of Miyako-jima.

[2] A stationary trough over China weakened the convection on the western periphery of the typhoon, and the eye gradually became less organized.

[nb 4][7] Before the typhoon affected Taiwan, residents in Taipei prepared sand bags,[8] and President Chen Shui-bian ordered the military to be on standby to assist in the storm's aftermath.

[9] Taiwan's Central Weather Bureau issued an offshore typhoon warning on July 2, prompting officials to cancel ferry service and restrict water activities in Kenting National Park.

[14] In contrast to the previously dry conditions on Taiwan, eastern China was experiencing above-normal rainfall, and many reservoirs were near capacity when Rammasun was approaching the region.

[18] Rammasun downed trees and caused power outages in the region, and storm flooding forced over 2,700 people to evacuate.

A station in Miyazaki Prefecture on the Japanese island of Kyushu reported the highest rainfall associated with Rammasun, with a total of 290 mm (11 in).

[24] Typhoon Rammasun passed a short distance west of Jeju-do, an island offshore South Korea,[4] dropping more than 300 mm (12 in) of rainfall.

[29] Later, Rammasun brought the average monthly rainfall in only two days in portions of Primorsky Krai, causing flooding along roads and riverways.