Gradually intensifying, Mindulle peaked as a Category 1-equivalent hurricane on the Saffir-Simpson scale on August 22 before making landfall in Chiba Prefecture later that day.

[1] A few hours later, the Joint Typhoon Warning Center (JTWC) quickly issued a Tropical Cyclone Formation Alert and also upgraded the system to a tropical depression with the designation 10W on the same day, based on increased symmetric convection associated with a defined but partially exposed low-level circulation center (LLCC) that was embedded within the southwest monsoon surge.

[2][3] One day later, the JTWC upgraded 10W to a tropical storm via the Dvorak technique, with the winds proved by a recent scatterometer pass.

[4] The JMA upgraded the system to a tropical storm and named it Mindulle early on August 19, when central convection had become more organized.

[6] Moving on the eastern edge of a relatively high-latitude monsoon gyre and being steered by the southern extension of the subtropical ridge anchored east of Japan, the intensification of Mindulle was limited on August 20, owing to modest dry air entrainment resulting in flaring convection near and surrounding the LLCC.

[7][8] Although the JMA upgraded Mindulle to a severe tropical storm when it was approximately 380 km (240 mi) northwest of Chichi-jima at around 15:00 JST (06:00 UTC) on August 21, outflow from Tropical Storm Lionrock to the west was inhibiting further development and causing a partially exposed LLCC with deep convection displaced southward, as the distance between their centers was only about 600 km (370 mi) at that time.

[13] While Mindulle was in its developmental stages, the Guam National Weather Service office issued a tropical storm watch for Tinian and Saipan.

[15] American military bases in Japan were set at Tropical Cyclone Condition of Readiness (TCCOR) 1, and non-essential people were directed to stay in their lodgings after most services were shut down.

[14] The offshore islands of Hachijō-jima and Izu Ōshima both reported 86 mm (3.4 in) of precipitation in just one hour, which is about half the average August rainfall for both locations.