Mindulle eventually reached Category 5 typhoon the next day, as the storm had a large eye in its center.

[4] On September 21, the Joint Typhoon Warning Center spotted an area of convection formed approximately 703 nmi (1,302 km; 809 mi) southeast of Guam.

[8] At 09:00 UTC of September 23, the JTWC upgraded it to a tropical storm, as its low-level circulation center became partially exposed.

[11] By 03:00 UTC the next day, the JTWC upgraded it to a Category 1-equivalent typhoon, as it developed a small eye.

Satellite imagery showed that the typhoon had developed a well defined 15 nmi (28 km; 17 mi) eye and deepening of the central core.

[15] At 15:00 UTC, Mindulle weakened into a Category 4-equivalent super typhoon as the eye and the convective structure started to degrade.

Its 20 nmi (37 km; 23 mi) eye had steadily shrunk but it remained cloud covered and ragged.