The 1991 Pacific typhoon season was a slightly above-average season with 29 tropical storms, 17 typhoons and five super typhoons forming. It was quite a catastrophic season – Typhoon Yunya impacted the Philippines in mid June while in the same time experiencing a volcanic eruption, Typhoon Mireille severely impacting Japan, which became known for being the costliest typhoon on record with US$10 billion worths of damages, and Tropical Storm Thelma on November which became one of the deadliest storms to strike the Philippines, killing at least over 5,000 people.

Typhoon Yunya, known in the Philippines as Typhoon Diding, was a strong tropical cyclone whose landfall in the Philippines coincided with the 1991 eruption of Mount Pinatubo. A small tropical cyclone, Yunya rapidly developed from a tropical disturbance near East Samar on June 11. By June 13 the storm had reached typhoon status as it moved west-northwest near the Philippines. Yunya attained its peak intensity the following day with estimated winds of 145 km/h (90 mph); however, strong wind shear soon impacted the typhoon and caused it to rapidly decay. The storm struck southern Luzon early on June 15 as a minimal typhoon before moving over the South China Sea later that day. After turning north and weakening to a tropical depression, the system brushed the southern tip of Taiwan on June 16 before dissipating the following day.