Convective activity increased in the monsoon trough that extended over the Caroline Islands on September 28. Post-analysis indicated the existence of a weak circulation southwest of Guam around that time, which was to become Tropical Storm Roger. On October 3, the system organized into Tropical Depression 21W, which was subsequently upgraded to a tropical storm and named "Roger" on October 4. Strong flow from the equator was drawn into Roger's circulation, preventing development to a disturbance to the east which would become Typhoon Tip. A strong mid-level southeasterly steering current caused Roger to move northwest. Roger then executed a cyclonic loop on October 5. The storm continued to move northwest until north of the ridge axis, after which it turned in a north-northeastward direction. Roger then became an extratropical cyclone on October 7, as it merged with a cold front south of Japan.