Overview of Tropical Cyclone in December 2021

Two tropical cyclones occurred over the western North Pacific and the South China Sea in December 2021. Among them, Rai necessitated the issuance of the tropical cyclone warning signals by the Observatory, which was the latest tropical cyclone warning signal in a year since 1946.

Nyatoh formed as a tropical depression over the western North Pacific about 360 km north-northeast of Yap on the early morning of 30 November. It moved west-northwestwards towards the seas east of the Philippines and intensified gradually. Nyatoh intensified into a severe tropical storm on the morning of 1 December. It then turned gradually to move northeastwards towards the vicinity of Iwo Jima and continued to intensify. Nyatoh further intensified into a super typhoon on the morning of 3 December and reached its peak intensity with an estimated maximum sustained wind of 185 km/h near its centre. Nyatoh weakened into a severe typhoon that night and finally evolved into an extratropical cyclone over the seas east of Iwo Jima.

Rai formed as a tropical depression over the western North Pacific about 2 680 km east-southeast of Manila on the night of 12 December. It moved west-northwestwards and intensified gradually. Rai started to intensify rapidly on 15 December and developed into a super typhoon on the next day. After sweeping across the Philippines, Rai weakened into a severe typhoon and moved westwards across the southern part of the South China Sea on 17 December. Rai re-intensified into a super typhoon the next day and became the first super typhoon over the South China Sea in December since 1961. It reached its peak intensity in the small hours on 19 December with an estimated maximum sustained wind of 205 km/h near its centre. Turning to move northeastwards gradually in the following two days, Rai edged closer to the coast of Guangdong and weakened rapidly. It finally degenerated into an area of low pressure over the seas south of Hong Kong on 21 December.

According to press reports, Rai left at least 409 deaths and over 100 000 people evacuated in the Philippines during its passage. For detailed information of Rai including its impact to Hong Kong, please refer to the Tropical Cyclone Report of Rai.