On November 23, a large area of convection persisted 650 km (400 mi) south of Pohnpei, near the equator or at latitude of 0.6ºN.
The system had a poorly-defined, elongated atmospheric circulation, and was located in an area of moderate wind shear and restricted outflow, due to a subtropical ridge to the north. As a result, the Joint Typhoon Warning Center (JTWC) assessed a low chance for tropical cyclogenesis.
The center slowly consolidated, with a well-defined mid-level circulation. Late on November 25, the JTWC issued a tropical cyclone formation alert after it organized further, noting that the system had developed an anticyclone which was providing outflow. Around the same time, the Japan Meteorological Agency (JMA) classified the system as a tropical depression, about 410 km (255 mi) south-southwest of Pohnpei. At 2100 UTC on November 25, the JTWC also upgraded the system to Tropical Depression 26W.
On November 27, a deep centralized convective cover developed over the LLCC and the JTWC too upgraded Bopha into a tropical storm. On November 28, a band of convection, associated with powerful thunderstorms formed south of Bopha, near the equator, which started to feed additional moisture into Bopha, which lead to it’s gradual increase in size. The band of convection became so large, and organize, that the band began to resemble a ‘tail’ as NASA stated.
On November 30, the JMA futher upgraded the system to a severe tropical storm, as it started to become better organize. As the system continued to intensify, organize bands of thunderstorms, began to develop rapidly around the system, mostly on the western half of the storm, which later merged with Bopha, which caused it to increase in size. Several hot towers also began to rise up near the low level circulation center, with on of the hot towers reaching 17 km (11 mi) into the atmosphere.
A few hours after the JMA upgraded the system into a severe tropical storm, the JTWC further upgraded the system to a Category 1 typhoon, at around 0600 (UTC). It began to explosively deepen over the day, becoming a category 4 storm 18 hours later still less than five degrees from the equator. Currently, Super Typhoon Bopha (STY 26W) is located approximately 195 nm east-southeast of Palau. It has tracked west-northwestward at 12 knots over the past six hours. Maximum significant wave height is 52 feet.