An area of convection, or thunderstorms, persisted west of Guam on September 13, in association with the monsoon trough.
The system gradually developed a low-level circulation and rainbands, aided by low wind shear from an anticyclone aloft.
Late on September 14, the Japan Meteorological Agency (JMA) designated the system as a tropical depression to the east of the Philippine island of Luzon.
Around the same time, the Joint Typhoon Warning Center (JTWC) classified the system as Tropical Depression 12W. A nearby tropical upper tropospheric trough limited the depression's outflow to the north, although convection continued to increase.
The depression moved northwestward along the southwestern periphery of a ridge.
At 03:00 UTC on September 15, the Philippine-based PAGASA began warning on the system, giving it the local name Inday.
Nine hours later, the JMA named the system Tropical Storm Fanapi.

As a strengthening tropical storm, Fanapi developed deeper convection near the center.
A passing trough to the north weakened the ridge and caused the storm to slow, turning northeastward by September 16.
That day, Fanapi developed an eye feature, becoming a typhoon at 18:00 UTC.
As the ridge built into the East China Sea, the storm responded by turning to the northwest, and at the same time, outflow improved to the north.
The eye organized further as it contracted to a diameter of 19 km (12 mi).
By that time, the typhoon was moving due westward toward Taiwan, steered by a ridge over northeastern China.
At 06:00 UTC on September 18, the JTWC estimated that Fanapi attained peak 1 minute winds of 195 km/h (120 mph).
Around the same time, the JMA estimated peak 10 minute winds of 175 km/h (110 mph).

Early on September 19, Typhoon Fanapi made landfall over eastern Taiwan near Hualien City with winds of 162 km/h (101 mph), according to Taiwan's Central Weather Bureau.
The storm subsequently weakened over land, dipping southwestward as convection diminished over the northern portion of the storm.
However, the storm resumed its westward trajectory and soon moved over the Taiwan Strait as a severe tropical storm.
The thunderstorms reorganized slightly as Fanapi reached open waters, and a nearby ship reported winds of 120 km/h (75 mph).
Early on September 20, the storm made a second landfall on southeastern China near Fujian and weakened further over land, although thunderstorms persisted southeast of the circulation along the coast.
Fanapi weakened into a tropical depression later that day and dissipated late on September 21.
An area of convection, or thunderstorms, persisted west of Guam on September 13, in association with the monsoon trough. The system gradually developed a low-level circulation and rainbands, aided by low wind shear from an anticyclone aloft. Late on September 14, the Japan Meteorological Agency (JMA) designated the system as a tropical depression to the east of the Philippine island of Luzon. Around the same time, the Joint Typhoon Warning Center (JTWC) classified the system as Tropical Depression 12W. A nearby tropical upper tropospheric trough limited the depression's outflow to the north, although convection continued to increase. The depression moved northwestward along the southwestern periphery of a ridge. At 03:00 UTC on September 15, the Philippine-based PAGASA began warning on the system, giving it the local name Inday. Nine hours later, the JMA named the system Tropical Storm Fanapi.
As a strengthening tropical storm, Fanapi developed deeper convection near the center. A passing trough to the north weakened the ridge and caused the storm to slow, turning northeastward by September 16. That day, Fanapi developed an eye feature, becoming a typhoon at 18:00 UTC. As the ridge built into the East China Sea, the storm responded by turning to the northwest, and at the same time, outflow improved to the north. The eye organized further as it contracted to a diameter of 19 km (12 mi). By that time, the typhoon was moving due westward toward Taiwan, steered by a ridge over northeastern China. At 06:00 UTC on September 18, the JTWC estimated that Fanapi attained peak 1 minute winds of 195 km/h (120 mph). Around the same time, the JMA estimated peak 10 minute winds of 175 km/h (110 mph).
Early on September 19, Typhoon Fanapi made landfall over eastern Taiwan near Hualien City with winds of 162 km/h (101 mph), according to Taiwan's Central Weather Bureau. The storm subsequently weakened over land, dipping southwestward as convection diminished over the northern portion of the storm. However, the storm resumed its westward trajectory and soon moved over the Taiwan Strait as a severe tropical storm. The thunderstorms reorganized slightly as Fanapi reached open waters, and a nearby ship reported winds of 120 km/h (75 mph). Early on September 20, the storm made a second landfall on southeastern China near Fujian and weakened further over land, although thunderstorms persisted southeast of the circulation along the coast. Fanapi weakened into a tropical depression later that day and dissipated late on September 21.
Typhoon Fanapi