late on july 23, an area of low pressure formed to the southeast of chuuk. the system gradually drifted to the west and on july 25, the jtwc upgraded the low pressure area to a tropical depression. at that time, it was about to the west of guam. at midnight, that day, the jma started monitoring the system as a tropical depression. early on july 28, the jtwc upgraded the system into a tropical storm. a few hours later, the jma too upgraded the system to a tropical storm, naming it "muifa". soon, the storm moved into the philippine area of responsibility (par), and the philippine atmospheric, geophysical and astronomical services administration (pagasa) named it "kabayan". the storm gradually drifted north over the next day maintaining strength. on the night of july 29, muifa was upgraded into a severe tropical storm. overnight, the storm strengthened rapidly and was upgraded into a typhoon the next morning. the storm strengthened so rapidly, and the jtwc reported that the storm's peak winds were reaching , as it strengthened into a category 5 typhoon. however, the typhoon could not maintain category 5 strength for a long time. according to the jtwc, on july 31, the typhoon interacted with an upper-level trough and weakened into a category 4 typhoon on the sshs. the system gradually moved north, then turned west and drifted towards okinawa, before turning northwest again, when it was finally downgraded into a tropical storm by the jtwc. soon afterwards, the jma too downgraded muifa to a severe tropical storm. after weakening to a tropical storm, muifa made landfall at the estuary of the yalu river on august 8, and the jtwc issued the final warning. early on august 9, muifa weakened to a tropical depression in northeast china and became a low pressure area later.