Part of the 2021 Pacific typhoon season, Kompasu originated from an area of low pressure east of the Philippines on 6 October 2021.

A day later, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) classified it as a tropical depression, naming it Maring.

At 18:00 UTC (Coordinated Universal Time) on 6 October 2021, the JMA noted that an area of low pressure embedded within a large monsoonal circulation had formed to the north of Palau.

[4] At 09:00 UTC (17:00 PHT) on 7 October, PAGASA issued its first bulletin for the depression, and assigned it the name Maring.

[5] The JMA also noted the persistence of another, nearby tropical depression to its Northeast, later named Nando.

[12] At midnight of 11 October, the JMA upgraded it to a severe tropical storm, as it attained good cloud characteristics.

[13] At 12:10 UTC (20:10 PHT) on 11 October, Kompasu made landfall on Fuga Island, Cagayan, as a severe tropical storm.

[18][19] At 09:00 UTC of the next day, the JTWC issued its final warning followed by downgrading to a tropical depression, as its convection had diminished and the low-level circulation center had been weakened significantly because of the increasing vertical wind shear and dry air, despite not making landfall over northern Vietnam.

[23] According to the National Disaster Risk Reduction and Management Council (NDRRMC), the storm affected 1,203,448 people in the regions of Ilocos, Cagayan Valley, Central Luzon, Calabarzon, Mimaropa, Caraga, Western Visayas, and the CAR.

[24] The Office of the Vice-president dispatched two squads to help those who were affected by the storm in the provinces of La Union, Cagayan, Isabela, and Benguet.

[2] The government of the Philippines distributed ₱17.9 million (US$352,000) worth of recovery items to people affected by the storm.

In Guangdong, a total of 30 cities and counties suspended classes, the highest since Typhoon Mangkhut in 2018.

[40] Despite weakened significantly before striking Vietnam, Kompasu still brought heavy rains to the Central region and caused flooding.

[42] The Central Weather Bureau issued advisories for heavy rain for northern and eastern parts of Taiwan.