Typhoon Omar originated from a tropical disturbance that was first noted on August 20 over the open Pacific Ocean, which exhibited persistent convection, or thunderstorms. During this early phase, two tropical cyclones dissipated and another became across the western Pacific basin; this caused the monsoon trough, which spawned most of the storms in the basin, to realign in a more climatologically appropriate manner. According to the Japan Meteorological Agency (JMA), Omar developed into a tropical depression at 1800 UTC on August 23. The Joint Typhoon Warning Center (JTWC) assessed a slower pace of strengthening, issuing a tropical cyclone formation alert at 2100 UTC before initiating advisories on Tropical Depression 15W on August 24.
As the depression traveled generally westward, the JTWC upgraded it to Tropical Storm Omar on August 25, and the JMA followed suit on the next day. Omar began to slow as it tracked westward. Outflow from nearby Tropical Storm Polly to the west produced a stream of strong wind shear over Omar, slowing intensification. The JTWC noted that the shear could decouple Omar's wind circulation from its convection, possibly weakening the storm. However, as Omar and Polly moved farther apart, a high-pressure ridge developed between the storms. This caused Omar to drift northward and then west-northwestward into a region with decreased shear, which allowed it to resume strengthening. Early on August 27, the JTWC upgraded the system to a typhoon, and an eye began to appear around 23:00 UTC that day. Omar entered a phase of rapid intensification on August 28, at which point the JMA also classified it as a typhoon. The typhoon made landfall on Guam soon after, with 1‑minute sustained winds of about 195 km/h (120 mph). The eye, 37 km (23 mi) in diameter, slowly crossed the northern portion of the small island over a period of 2.5 hours.
At 1800 UTC on August 29, Omar reached its peak intensity with 10‑minute sustained winds of 185 km/h (115 mph) and a minimum barometric pressure of 920 mbar (hPa; 27.17 inHg) as estimated by the JMA; this intensity was maintained for 24 hours before a steady weakening trend began. The JTWC estimated higher 1‑minute winds of around 240 km/h (150 mph), making Omar a super typhoon. Two days later, the typhoon came close enough to the Philippines to warrant monitoring from PAGASA,[nb 3] who named the storm Lusing. By 1500 UTC on September 3, the JMA downgraded Omar to a tropical storm, although the JTWC maintained its typhoon intensity through the next day. Heading generally westward, the storm made landfall on the east coast of Taiwan near Hualien City on September 4. After traversing the island in seven hours, Omar exited the coast of Yunlin County and emerged into the Taiwan Strait. The storm crossed the body of water and moved ashore in eastern China near Xiamen, Fujian, on September 5. Inland, Omar quickly degenerated into a tropical depression before turning west-southwest. It proceeded across southern China while heavily weakening, and completely dissipated over northern Vietnam on September 9.