Attachments
2.1 Review of tropical cyclones in 2008
2.1.1 Tropical cyclones over the western North Pacific (including the South China Sea)
In 2008, 24 tropical cyclones affected the western North Pacific and the South China Sea (i.e. the area bounded by the Equator, 45°N, 100°E and 180°). In the past 4 years (2005-2008), the annual number of tropical cyclones in this ocean basin has been less than the 30-year (1971-2000) average of 30. Throughout the year, 11 tropical cyclones attained typhoon strength, about 4 less than the normal figure.
The first tropical cyclone of the year formed in April. Figure 2.1 shows the monthly frequencies of the occurrence of tropical cyclones in the western North Pacific and the South China Sea in 2008.
During the year, eight tropical cyclones hit mainland China, four crossed over Taiwan, one skirted the coastal areas of southern Japan and the Ryukyu Islands, one made landfall over DPR Korea, three traversed the Philippines and another five made landfall over Vietnam.
The most intense tropical cyclone in 2008 was Jangmi (0815), which had a maximum wind speed of about 230 km/h and a minimum sea-level pressure of about 905 hPa (Table 4.1) when it was located over the western North Pacific to the east-southeast of Taiwan (Fig. 2.7).
The “Na Lina” phenomena over the Pacific occurred in early 2008 when the sea temperatures over the eastern and central equatorial Pacific were below normal. In the second half of the year, the “Nina Lina” conditions had weakened but the sea temperatures in the central Pacific were still slightly below normal. Furthermore, the subtropical ridge of high pressure over the western North Pacific was stronger than normal in summer and autumn, suppressing the convection over the area. Affected by such climatic conditions, the activity of the tropical cyclones in the western North Pacific and the South China Sea in 2008 was more concentrated over the western part of the region with 20 tropical cyclones formed in the region west of 140°E and only four to the east of 140°E. In addition, there were more tropical cyclones bringing gale force winds to Hong Kong and the typhoon season in Hong Kong started earlier than normal.
2.1.2 Tropical cyclones in Hong Kong’s area of responsibility
Amongst the 24 tropical cyclones in 2008, 17 occurred inside Hong Kong’s area of responsibility (i.e. the area bounded by 10°N, 30°N, 105°E and 125°E), more than the 30-year (1971-2000) annual average of 15.4 (Table 2.1). Eight of these 17 tropical cyclones developed within Hong Kong’s area of responsibility. Altogether, 472 tropical cyclone warnings to ships and vessels were issued by the Hong Kong Observatory in 2008 (Table 4.2).
2.1.3 Tropical cyclones over the South China Sea
Eleven tropical cyclones affected the South China Sea (i.e. the area bounded by 10°N, 25°N, 105°E and 120°E) in 2008. Six of them formed over the area. Five moved into the area from the western North Pacific.
2.1.4 Tropical cyclones affecting Hong Kong
In 2008, the typhoon season started on 17 April when Typhoon Neoguri came within 800 km and necessitated the issuance of the Standby Signal No. 1. This was the second earliest onset time since 1946 (The earliest time of 9 April was set in 1967).
Six tropical cyclones, namely Typhoon Neoguri (0801) in April, Typhoon Fengshen (0806) in June, Severe Tropical Storm Kammuri (0809) and Typhoon Nuri (0812) in August, Typhoon Hagupit (0814) in September and Tropical Storm Higos (0817) in October affected Hong Kong (Figure 2.2), which was close to the normal number of 6 to 7 (Table 2.2). However, four of them, Fengshen, Kammuri, Nuri and Hagupit necessitated the issuance of the No. 8 Gale or Storm Signal or higher signals in Hong Kong, higher than the normal of one to two per year, and making 2008 the year with the most No. 8 Signals since 1999.
The centre of Nuri crossed Hong Kong in August 2008 and necessitated the issuance of the Increasing Gale or Storm Signal No. 9, the highest signal issued in 2008. Neoguri in April and Higos in October only necessitated the issuance of the Strong Wind Signal No. 3 and the Standby Signal No. 1 in Hong Kong respectively.
During the passage of Hagupit, the combined effect of storm surges and high tides resulted in a maximum sea level of 3.53 metres at Quarry Bay, the highest since Typhoon Wanda in September 1962.
2.1.5 Tropical cyclone rainfall
Tropical cyclone rainfall (the total rainfall recorded at the Hong Kong Observatory from the time when a tropical cyclone is centred within 600 km of Hong Kong to 72 hours after it has dissipated or moved farther than 600 km away from Hong Kong) in 2008 was 1,096.6 mm (Table 4.8.1). This is 47% above the normal of 745.5 mm and accounts for some 36% of the year’s total rainfall of 3,066.2 mm.
Fengshen which affected Hong Kong on 23-25 June brought 342.6 mm of rainfall to Hong Kong, which was the tropical cyclone bringing the most rainfall to Hong Kong in 2008. Over 200 mm of rainfall were also recorded at the Hong Kong Observatory during the passages of Neoguri and Kammuri.
2.2 Monthly overview
A monthly overview of tropical cyclones is given in this section. Detailed reports on tropical cyclones affecting Hong Kong are presented in Section 3.