Typhoon Choi-wan was a powerful typhoon that became the first Category 5-equivalent super typhoon to form during the 2009 Pacific typhoon season. Forming on September 11, 2009, about 1,100 km (700 mi) to the east of Guam, the initial disturbance rapidly organized into a tropical depression. By September 12, the depression intensified into a tropical storm, at which time it was given the name Choi-wan. The following day, rapid intensification took place through September 14. Choi-wan attained its peak intensity on September 15, as it moved through the Northern Mariana Islands with the Japan Meteorological Agency reporting peak 10-minute sustained winds of 195 km/h (121 mph). Additionally, the Joint Typhoon Warning Center reported the storm to have attained 1-minute sustained winds of 260 km/h (160 mph). The typhoon remained very powerful until September 17 when the storm's outflow weakened. The typhoon underwent an eyewall replacement cycle, leading to intensity fluctuations. By September 19, Choi-wan rapidly weakened as strong wind shear caused convection to diminish. The following day, the system transitioned into an extratropical cyclone and dissipated several hours later over open waters.

Alamagan is an island in the Northern Mariana Islands in the Pacific Ocean, 30 nautical miles (56 km) north of Guguan, 250 nautical miles (463 km) north of Saipan, and 60 nautical miles (111 km) south of Pagan. It is currently undergoing resettlement since 2018, with a few people living there. The project was coordinated by the Northern Islands Mayor's office and the people there have radio contact with the mainland.