Fujiwhara effect
On September 6, a Monsoonal trough quickly spawned an Embedded depression that became a tropical storm on September 9. However, due to the Fujiwhara effect, the much stronger system, Typhoon Saomai dragged Bopha approximately 1,550 kilometers south, and weakened Bopha from September 9–11. The remnants of Bopha continued to move eastwards as it became Severe Tropical Storm Sonamu on September 15.