On August 6, the Japan Meteorological Agency (JMA) began monitoring an area of disturbed weather in the vicinity of the Federated States of Micronesia. By early the next day, satellite imagery indicated the presence of a small circulation north of Chuuk. Radars at Fleet Weather Central and Andersen Air Force Base on Guam detected spiral convective bands crossing the island on August 9. At 00:00 UTC the following day, the system developed into Tropical Storm Rose while located west of Guam. Around that time, a reconnaissance aircraft flight indicated a "mini-storm" with sustained winds between . Initially, Rose moved west-northwestward at about . The storm was a small cyclone, covering an area of . Rose quickly strengthened and became a typhoon around 12:00 UTC on August 10. Early the following day, the system briefly weakened back to a tropical storm, before re-acquiring typhoon status hours later.