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Royal Observatory Hong Kong: Tropical Cyclones in 1987

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In 1987, only 26* tropical cyclones affected the western North Pacific and the South China Sea bounded by the equator, 45o N, 100o E and 180o . This number falls below the annual average (1951-1980) of 32 tropical cyclones in the region. Seventeen of them attained typhoon intensity, which was slightly higher than the annual average of sixteen.

The tropical cyclones in 1987 in the western North Pacific were characterized by their tendency to form in the eastern part of the region and their subsequent northward movement. As a result, only nine tropical cyclones affected the South China Sea. This is the fewest since 1976. Among these, only two actually formed within this part of the ocean basin, one in June and the other in November. Since 1975, this is the first year when no tropical cyclone occurred in the South China Sea during the month of July. A total of six tropical cyclones traversed the Philippines. Among those that made landfall, three were over the mainland of China, three crossed or passed close to Taiwan, four over Vietnam, one over Korea and one over Japan, None of the tropical cyclones came close enough to affect Hong Kong significantly.

The monthly distribution of the frequency of first occurrence of tropical cyclones and that of typhoons for 1987 are shown in Figure 2 and a brief summary is contained in Table 1. Six-hourly positions of these tropical cyclones together with their estimated minimum central pressures and maximum sustained surface winds are tabulated in Section 5. The monthly mean frequencies of these two parameters during the years 1951-1980 are shown in Figure 3.

During the year, 13 tropical cyclones occurred within the area of responsibility of Hong Kong for tropical cyclone warnings for shipping, (i.e. the area bounded by 10o N, 30o N, 105o E and 125o E) compared with the 30-year annual average of 17. Eleven† tropical cyclones moved into this area and two developed within it.

Altogether 336 warnings for shipping were issued by the Royal Observatory in connection with these tropical cyclones.

Tropical cyclone warning signals were displayed in Hong Kong for 5 tropical cyclones. Only Typhoon Lynn necessitated the hoisting of the Strong Wind Signal No. 3.

The total tropical cyclone rainfall (defined as the total rainfall recorded at the Royal Observatory, Hong Kong from the first day when a tropical cyclone was centred within 600 km of Hong Kong to the end of the third day after the tropical cyclone has dissipated or moved outside 600 km of Hong Kong) during 1987 amounted to 193.2 mm, which is 34 per cent of the annual average value of 566.9 mm (18841939 and 1947-1970). It accounted for only 8 per cent of the year's total rainfall of 2 319.3 mm. Four tropical cyclones came within 600 km of Hong Kong. Typhoon Nina (8722), for which no warning signals were hoisted in Hong Kong, brought 54.7 mm of rainfall. Rainfall figures associated with the three other tropical cyclones are given in Table 8.

Typhoon Norris (8629), which crossed the central Philippines late in December 1986, weakened and turned northwestwards on entering the South China Sea. It eventually dissipated about 360 km north-northeast of Nansha early on 2 January.

Orchid (8701) was the first tropical cyclone to form in 1987. It formed as a tropical depression about 180 km southwest of Truk on the evening of 8 January. Moving west-northwestwards, Orchid became a typhoon early on 11 January about 140 km east-northeast of Yap. Later that morning, it passed about 80 km north of the island.

Under the influence of the northeast monsoon, Orchid turned south-southwestwards and weakened to a tropical storm on 13 January about 1 210 km east-southeast of Manila. It dissipated on 14 January about 380 km east of Mindanao.

Almost three months later, Tropical Depression Percy (8702) formed over the Pacific about 650 km east of Yap on 10 April. It intensified to a tropical storm the next morning. However, it was rather short-lived as it dissipated on the morning of 13 April about 240 km north-northwest of Yap.

Two more months passed before another tropical cyclone formed. This was the first one to develop over the South China Sea in 1987. On the morning of 18 June, a tropical depression formed about 260 km southwest of Dongsha, and intensified to Tropical Storm Ruth (8703) while moving northwestwards. The next morning, it crossed the south China coast between Yangjiang and Zhanjiang about 290 km west-southwest of Hong Kong while moving on a west-northwestward course. Soon after landfall, Ruth reached its maximum intensity and then weakened into a tropical depression and eventually dissipated about 80 km northwest of Nanning on the morning of 20 June. Extensive damage was inflicted in the provinces of Guangdong and Guangxi of China.