Eye of Typhoon Muifa (11W) – August 4th, 201128.5N 128.9E
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 located approximately 505 nautical miles (935 km; 581 mi) 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 (11W).
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 140 knots (260 km/h; 160 mph) (1-min sustained), as it strengthened into a Category 5 Typhoon.
However, the typhoon couldn’t 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.