Typhoon Usagi Rapidly Intensifies to Equivalent of a Major Hurricane

Typhoon Usagi rapidly intensified to the equivalent of a major hurricane over the Western North Pacific Ocean east of Luzon on Wednesday.  At 10:00 a.m. EST on Wednesday the center of Typhoon Usagi was located at latitude 16.5°N and longitude 124.8°E which put the center about 485 miles (780 km) east-southeast of Aparri, Philippines.  Usagi was moving toward the west-northwest at 15 m.p.h. (24 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 949 mb.

Typhoon Usagi rapidly intensified to the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale east of Luzon on Wednesday.  A small circular eye with a diameter of 5 miles (8 km) formed at the center of Usagi’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 revolved around the core of Typhoon Usagi.  Storms near the core of Usagi generated strong upper level divergence that pumped large quantities of mass away from the typhoon in all directions.  The removal of large amounts of mass caused the surface pressure to decrease rapidly.

The circulation around Typhoon Usagi was small.  Winds to typhoon force extended out 30 miles (50 km) from the center of Usagi’s circulation.  Winds to tropical storm force extended out 80 miles (130 km) from the center of Typhoon Usagi.

The Hurricane Intensity Index (HII) for Typhoon Usagi was 25.1.  The Hurricane Size Index (HSI) was 9.4 and the Hurricane Wind Intensity Size Index (HWISI) was 34.5.  Typhoon Usagi was similar in size to Hurricane Harvey when Harvey hit Texas in 2017.  Usagi was not as big as Harvey was.

Typhoon Usagi will move through an environment favorable for intensification during the next 24 hours.  Usagi will move over water where the Sea Surface Temperatures are near 30°C.  It will move under the axis of an upper level ridge over the Western North Pacific Ocean.  The upper level winds are weak near the axis of the ridge and there will be little vertical wind shear.  Typhoon Usagi could continue to intensify during the next 24 hours.  However, since the core of Usagi’s circulation is so small, the inner end of a rainband could wrap around the core.  If concentric eyewalls form, an eyewall replacement cycle would halt the intensification of Typhoon Usagi.

Typhoon Usagi will move around the southern side of a high pressure system over the Western North Pacific Ocean.  The high pressure system will steer Usagi toward the west-northwest during the next 24 hours.  On its anticipated track, the center of Typhoon Usagi will move near northeast Luzon in 18 hours.

Typhoon Usagi will bring strong winds and heavy rain to northern Luzon.  Heavy rain could cause flash floods and mudslides in some locations.  Usagi could cause a storm surge of up to 13 feet ( 4 meters) on the coast of northeastern Luzon.  The area likely to be hit by Usagi was just hit by Typhoon Toraji a few days ago.  Typhoon Usagi will complicate recovery efforts in Luzon.

Elsewhere over the Western North Pacific Ocean, Tropical Storm Toraji was approaching the coast of China east of Hong Kong, and Tropical Storm Man-yi was moving away from the Marianas.

At 10:00 a.m. EST on Wednesday the center of Tropical Storm Toraji was located at latitude 21.9°N and longitude 114.9°E which put the center about 65 miles (105 km) east-southeast of Hong Kong.  Toraji was moving toward the north at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 995 mb.

At 10:00 a.m. EST on Wednesday the center of Tropical Storm Man-yi was located at latitude 11.7°N and longitude 140.4°E which put the center about 280 miles (450 km) west-southwest of Guam.  Man-yi was moving toward the west-southwest at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1002 mb.