During September 11, both the JMA and the JTWC started to monitor Tropical Depression 18W approximately south of Hagåtña, Guam. Due to decent organization and improved banding, JTWC upgraded 18W to a tropical storm. 18W was fully upgraded to a named tropical storm by the JMA few hours later and was named Malakas. By September 13, Malakas had improved in its organization and was already strengthening with deep convection wrapping into its LLCC; the JMA upgraded Malakas to a severe tropical storm thereafter. In the same time, Malakas had entered the Philippine area of Responsibility, with PAGASA assigning the local name Gener. Later, it was reported that Malakas was located in marginal conditions for further development due to wind shear caused by the proximity of the outflow of Typhoon Meranti. However the JMA upgraded Malakas to a typhoon three hours later. With improving conditions, it was reported that a cold dense overcast was forming and the JTWC upgraded Malakas to a Category 1 typhoon during the next day. By September 15, Malakas was over in very favorable conditions of Sea surface temperature of nearly and was later upgraded to a Category 2 typhoon. After maintaining this intensity for six hours, satellite imagery depicted an improved deep convection and a well-defined eye feature, as Malakas rapidly intensified into a Category 4 typhoon. Malakas reached its peak intensity with 1-minute sustained winds of 215 km/h and a minimum pressure of 930 hPa. The JMA had 10-minute sustained winds of 175 km/h on midnight of September 17. Shortly thereafter, its eye became cloud-filled and ragged and weakened to a Category 3 typhoon. Later in that same day, Malakas further weakened to a Category 2 as satellite imagery depicted warming cloud tops, decreasing convection and SSTs of only around. However, by September 18, Malakas started to re-intensify as it moved east-northeastward. Malakas reached its secondary peak intensity on September 19, but only as a Category 3 typhoon. Malakas then started to weaken due to land interaction with Japan. On September 20, the JTWC downgraded Malakas to a tropical storm, while the JMA downgraded it to a severe tropical storm, because at around 00:00 JST on September 20, Malakas made landfall over the Ōsumi Peninsula in Japan. It subsequently crossed Cape Muroto at around 11:00 JST and made landfall over Tanabe at around 13:30 JST. Both agencies issued their final advisory later that day as it became extratropical.
