The eighth tropical storm in the western Pacific that year, Koni originated from a disturbance situated within the monsoon trough well east of the Philippines on July 15.

Tracking westward, intensification was slow and the system remained a tropical depression as it moved across the central Philippines on July 17.

Upon moving into the South China Sea, however, conditions allowed for quicker strengthening, and as such the cyclone reached tropical storm status on July 18 before reaching its peak intensity with maximum sustained winds of 110 km/h (68 mph) and a minimum barometric pressure of 975 mbar (hPa; 28.79 inHg),[nb 2] making it a severe tropical storm.

The tropical storm continued to weaken as it moved over the Gulf of Tonkin prior to a final landfall near Hanoi, Vietnam the following day.

After moving into the South China Sea, turbulence produced by the storm resulted in an aviation incident involving a commercial airliner off the western Philippines.

Widespread power outages occurred, and strong winds resulted in agricultural and infrastructural damage, particularly in Vietnam's northern provinces.

[1] This prompted the Japan Meteorological Agency (JMA) to classify the system as a tropical depression at 0000 UTC on July 15, well north of Palau.

[1] This indicated an increase in intensity, and as such Koni reached a peak in strength at 1800 UTC that day with maximum sustained winds of 110 km/h (68 mph) and a minimum barometric pressure of 975 mbar (hPa; 28.79 inHg).

[3] After a brief reemergence into the Gulf of Tonkin, the system made another landfall, this time south of Hanoi, Vietnam at 0800 UTC on July 22.

Upon tracking inland, the storm began to quickly weaken, and was downgraded to tropical depression intensity at 1800 UTC that day over northern Laos.

[5] On July 18, an Airbus A330-242 carrying 242 passengers bound for Hong Kong encountered Koni in the South China Sea and attempted to deviate from its planned trajectory in order to avoid severe weather.

Ultimately effects in the Hong Kong area were limited to scattered squally weather producing isolated rainfall peaking at over 40 mm (1.6 in) in some locations.

Offshore the northern coast of Vietnam, 19 fishing and passenger boats capsized due to strong waves produced by the tropical storm.

Further north, in Thái Bình, gusts reaching as high as 90 km/h (56 mph) damaged 250 residences as well as 300 hectares (740 acres) of rice crops.