Typhoon Koinu (2023): A Comprehensive Retrospective
1. Formation and Meteorological History
Typhoon Koinu, known in the Philippines as Typhoon Jenny, formed as a tropical depression over the western North Pacific Ocean on September 28, 2023, approximately 1,920 km east of Manila. It gradually intensified while moving westward, becoming a severe typhoon on October 2 with maximum sustained winds of 175 km/h (109 mph). Koinu reached peak intensity as a Category 4-equivalent storm before making landfall over southern Taiwan on October 5. After crossing Taiwan, it weakened but reintensified over the South China Sea, reaching severe typhoon status again on October 6. The storm then moved slowly toward the Pearl River Estuary, but rapidly weakened due to the northeast monsoon, degenerating into a low-pressure area over the coastal waters of Yangjiang on October 9.
2. Impact and Damages
Taiwan: Koinu brought destructive winds and torrential rains to southern Taiwan. One person was killed, 399 were injured, and over 460,000 households experienced power outages. Water supply was disrupted for more than 6,000 households, and around 3,000 people were displaced. Agricultural and infrastructure losses exceeded USD 18 million.
Hong Kong: The Hong Kong Observatory issued the Increasing Gale or Storm Signal No. 9, the second such signal in 2023. Koinu brought record-breaking rainfall: 369.7 mm fell on October 9, more than three times the monthly normal for October. The 24-hour rainfall from October 8-9 reached 439.8 mm, the highest October record. Widespread flooding and landslides occurred.
Macao: Two people were injured, and 19 incidents were reported, including fallen trees and a landslide.
Philippines: Although Koinu did not make landfall, it enhanced the southwest monsoon, causing heavy rains and flooding in parts of Luzon. No direct casualties were reported.
Mainland China: Coastal areas of Guangdong experienced strong winds and heavy rain, but damage was limited due to the storm's rapid weakening.
3. Government Response and Relief Efforts
Taiwan: The Central Emergency Operation Center activated, coordinating evacuations and deploying military resources for rescue and recovery. Power companies worked to restore electricity, and disaster relief funds were allocated.
Hong Kong: The Hong Kong Observatory issued timely warnings, and the Home Affairs Department opened temporary shelters. The Drainage Services Department deployed flood prevention measures.
Macao: The Meteorological and Geophysical Bureau issued warnings, and the Civil Protection Operation Centre activated. Emergency services responded to incidents.
Philippines: The National Disaster Risk Reduction and Management Council (NDRRMC) monitored the enhanced monsoon and issued advisories. Preemptive evacuations were conducted in flood-prone areas.
International: The Joint Typhoon Warning Center (JTWC) and regional meteorological agencies provided forecasts and warnings, facilitating preparedness across affected regions.