Typhoon Lan rapidly intensified to the equivalent of a major hurricane over the Western North Pacific Ocean south of Japan on Thursday. At 11:00 p.m. EDT on Thursday the center of Typhoon Lan was located at latitude 27.1°N and longitude 142.8°E which put it about 615 miles (995 km) south-southeast of Tokyo, Japan. Lan was moving toward the north at 6 m.p.h. (10 km/h). The maximum sustained wind speed was 130 m.p.h. (210 km/h) and there were wind gusts to 160 m.p.h. (260 km/h). The minimum surface pressure was 936 mb.

Typhoon Lan intensified to the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale on Thursday. A circular eye with a diameter of 28 miles (45 km) developed at the center of Lan’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the core of Typhoon Lan. Storms near the core generated upper level divergence that pumped mass away from the typhoon in all directions. The removal of large quantities of mass caused the surface pressure to decrease rapidly.

The size of the circulation around Typhoon Lan increased when Lan intensified rapidly on Thursday. Winds to typhoon force extended out 45 miles (75 km) from the center of Lan’s circulation. Winds to tropical storm force extended out 160 miles (260 km) from the center of circulation. The Hurricane Intensity Index (HII) for Typhoon Lan was 25.1. The Hurricane Size Index (HSI) was 14.0 and the Hurricane Wind Intensity Size (HWISI) was 39.1. Typhoon Lan was similar in size and intensity to Hurricane Harvey when Harvey hit Texas in 2017.

Typhoon Lan will move through an environment favorable for intensification during the next 24 hours. Lan will move over water where the Sea Surface Temperatures are near 28°C. It will move through a region where the upper level winds are weak and there will be little vertical wind shear. Typhoon Lan is likely to intensify during the next 24 hours unless the inner end of a rainband wraps around the existing eye and eyewall. If concentric eyewalls form, then an eyewall replacement cycle could cause Typhoon Lan to weaken.

Typhoon Lan will move around the western part of a high pressure system over the Western North Pacific Ocean. The high pressure system will steer Lan toward the northwest during the next 24 hours. On its anticipated track, Typhoon Lan will bring strong, gusty winds and locally heavy rain to Chichi Jima during the next 24 hours. Typhoon Lan could approach Honshu in four days.

Elsewhere over the Western North Pacific Ocean, former Tropical Storm Khanun produced gusty winds and locally heavy rain over South Korea. At 5:00 p.m. EDT on Thursday the center of Tropical Depression Khanun was located at latitude 38.9°N and longitude 127.0°E which put it about 85 miles (135 km) north-northeast of Seoul, South Korea. Khanun was moving toward the northwest at 9 m.p.h. (15 km/h). The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 994 mb.