Typhoon Lan, known in the Philippines as Super Typhoon Paolo, was the third-most intense tropical cyclone worldwide in 2017. A very large storm, Lan was the twenty-first tropical storm and ninth typhoon of the annual typhoon season. It originated from a tropical disturbance that the United States Naval Research Laboratory had begun tracking near Chuuk on October 11. Slowly consolidating, it developed into a tropical storm on October 15, and intensified into a typhoon on October 17. It expanded in size and turned northward on October 18, although the typhoon struggled to intensify for two days. On October 20, Lan grew into a very large typhoon and rapidly intensified, due to favorable conditions, with a large well-defined eye, reaching peak intensity as a "super typhoon" with 1-minute sustained winds of 249 km/h (155 mph) – a high-end Category 4-equivalent storm – late on the same day. Afterward, encroaching dry air and shear caused the cyclone to begin weakening and turn extratropical, before it struck Japan on October 23 as a weaker typhoon. Later that day, it became fully extratropical before it was absorbed by a larger storm shortly afterward.