The system gradually organized and improved its outer bands, which prompted JTWC to give its identifier as Tropical Depression 18W.

Shortly after it reached its peak intensity, Malakas started to gradually weaken, downgraded back to Category-2 typhoon.

During September 11, both the JMA and the JTWC started to monitor Tropical Depression 18W approximately 58 km (36 mi) south of Hagåtña, Guam.

[8] 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.

[10] 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.

[11] By September 15, Malakas was over in very favorable conditions of Sea surface temperature (SSTs) of nearly 30 °C (86 °F) and was later upgraded to a Category 2 typhoon.

[12][13] After maintaining this intensity for six hours, satellite imagery depicted an improved deep convection and a well-defined 10 nmi (19 km; 12 mi) eye feature, as Malakas rapidly intensified into a Category 4 typhoon.

[16] 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 28 °C (82 °F).

[26][27] Malakas passed about 81 mi (130 km) to the east of Taipei on September 17,[28] producing heavy rain and strong winds to northern Taiwan.