Attachments
2.1 Review of tropical cyclones in 2006
2.1.1 Tropical cyclones over the western North Pacific (including the South China Sea)
In 2006, 27 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°), with one of them formed over the central part of the North Pacific and crossed the International Date Line into the western North Pacific. In the past 9 years (1998-2006), with the exception of 2004, the annual number of tropical cyclones in this ocean basin has been less than the 30-year (1961-1990) average of 31. Throughout the year, 14 tropical cyclones attained typhoon strength, two less than the normal figure.
The first tropical cyclone of the year formed in March. The monthly frequencies of the occurrence of tropical cyclones in the western North Pacific and the South China Sea in 2006 are shown in Figure 2.1.
During the year, seven tropical cyclones hit mainland China, three affected Taiwan, four affected Japan (including Ryukyu Islands), one made landfall over South Korea, seven traversed the Philippines, another three made landfall over Vietnam.
The most intense tropical cyclone in 2006 was Saomai (0608). Saomai had a maximum wind speed of about 215 km/h and a minimum sea-level pressure of about 920 hPa when it was located over the sea to the northeast of Taiwan.
Cimaron (0619) was the tropical cyclone with the most peculiar track in 2006. After forming over the western North Pacific on 27 October, Cimaron generally took on a west-northwesterly course under the influence of the westerly steering current south of the upper subtropical ridge of high pressure. Following the weakening of the upper subtropical ridge over the South China Sea, Cimaron became almost stationary from 1 to 2 November. Thereafter, Cimaron turned south-southwestwards and dissipated over the South China Sea under the influence of the intense northeast monsoon.
2.1.2 Tropical cyclones in Hong Kong’s area of responsibility
Amongst those 27 tropical cyclones in 2006, 16 occurred inside Hong Kong’s area of responsibility (i.e. the area bounded by 10°N, 30°N, 105°E and 125°E). This was near the 30-year (1961-1990) annual average of 16.4 (Table 2.1). Five of these 16 tropical cyclones developed within Hong Kong’s area of responsibility. Altogether, 460 tropical cyclone warnings to ships and vessels were issued by the Hong Kong Observatory in 2006 (Table 4.2).
2.1.3 Tropical cyclones over the South China Sea
There were 13 tropical cyclones affecting the South China Sea (i.e. the area bounded by 10°N, 25°N, 105°E and 120°E) in 2006. Four of them formed over the area. Nine moved into the area from the western North Pacific.
2.1.4 Tropical cyclones affecting Hong Kong
Seven tropical cyclones affected Hong Kong in 2006 (Figure 2.2), which is near normal (Table 2.2). These seven tropical cyclones were Chanchu (0601), Jelawat (0602), Prapiroon (0606), Bopha (0609), the tropical depressions in August and September and Cimaron (0619).
The highest signal issued this year was Strong Wind Signal No. 3 when Chanchu, Prapiroon and the tropical depression affected Hong Kong in May, August and September respectively.
Jelawat in June, Bopha and the tropical depression in August and Cimaron in October to November only necessitated the issuance of the Standby Signal No. 1 in Hong Kong.
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 2006 was 1 007.3 mm. This is 37% above the normal of 737.9 mm and accounts for some 38% of the year’s total rainfall of 2 627.8 mm.
The tropical depression which affected Hong Kong on 12-13 September brought 265.6 mm of rainfall to Hong Kong, which was the tropical cyclone bringing the most rainfall to Hong Kong in 2006.