Late on October 11, the JTWC began monitoring a scattered area of moderate convection within a broad low-level center 280 km (170 mi) west-southwest of Manila, Philippines.

[1] Within a marginally favorable environment of no distinct outflow established, low to moderate wind shear, and warm sea surface temperatures, the system slightly organized by the next day, with flaring convection and its center remaining exposed.

[6] Sonca failed to intensify further as its center remained exposed, with deep convection displaced to the west due to strong wind shear,[7] and it soon made landfall on Da Nang, Vietnam late on the same day, prompting the JTWC to issue their final advisory on the system.

[9] As Sonca moved inland, it brought heavy rainfall to central Vietnam, with 700 mm (28 in) of rain fell in Da Nang during a 24-hour period on October 14–15; this resulted in major flooding throughout the region.

[10] Initial estimated economic losses in Da Nang City caused by Sonca's heavy precipitation are around 1.48 trillion VND (US$60.8 million).