ENG-1980 — Page 293

218

THE ENVIRONMENT

Climate Although Hong Kong lies in the tropics it has a remarkably temperate climate for nearly half the year. The best months are usually November and December when there are pleasant breezes and comfortable temperatures, with plenty of sunshine. During January and February there is relatively more cloud and occasional cold fronts followed by cold dry northerly winds which, at times, can be too cold for comfort. It is not uncommon then for temperatures to drop below 10°C, and ice is occasionally reported in the New Territories. March and April can also be very pleasant except for occasional spells of fog, drizzle and high humidity which can be particularly unpleasant on high ground exposed to the south-east.

May and June are hot and humid with frequent showers and thunderstorms occurring mostly in the mornings; afternoon temperatures often exceed 32°C. At night, temperatures generally remain around 26°C with high humidity.

There is usually a fine spell in early July which may last for one or two weeks.

An average of 13 tropical cyclones of various intensities enter the South China Sea each year, mostly between July and October. About five of them become typhoons - that is, the wind speeds near the centres exceed 64 knots. Fully-developed tropical cyclones generally have relatively calm eyes averaging 50 kilometres in diameter surrounded by walls of cloud about 20 kilometres thick. Inside the cloud walls the strongest winds rotate anti-clockwise and the heaviest rain occurs. Outside them, bands of cloud and rain spiral in some 500 to 1,000 kilometres towards the centre.

Tropical cyclones occur in the Pacific and South China Sea throughout the year but none has ever caused gales in Hong Kong during the period from December to April. When a tropical cyclone is about 700-1,000 kilometres south-east of Hong Kong the weather is usually fine and exceptionally hot. Thunderstorms sometimes occur in the evenings. If the centre moves closer to Hong Kong, the wind increases and rain can become heavy and widespread. Heavy rain from tropical cyclones lasts from one to three days and sometimes can cause more damage than the winds.

The mean annual rainfall is 2,246 millimetres, of which about 80 per cent falls between May and September. The wettest month is June when rain occurs about two days out of three and the average monthly rainfall is 457.5 millimetres. The driest month is December when the monthly average is only 25.9 millimetres and rain usually falls on only about five days in the month. October is the sunniest month when an average of 58 per cent of possible hours of sunshine is recorded. Climatological information on Hong Kong's weather is given in Appendix 39.

Severe weather phenomena that can affect Hong Kong include tropical cyclones between May and November, strong winds from the winter monsoon between October and March, frost and ice on hills and inland in the New Territories between December and February, and thunderstorms that are most frequent from April to September. Water-spouts, hail- storms and snow are rare. Although the lowest temperature recorded at the Royal Observatory in Tsim Sha Tsui was 0°C, sub-zero temperatures are recorded at times at higher elevations and in the New Territories.

The Year's Weather

The year 1980 was generally hot and dry with the level of rainfall reaching only 1,710.6 millimetres compared with a normal of 2,246.4 mm. To a large extent this shortfall was due to the remarkably hot and dry weather experienced in the month of June. The number of tropical cyclones in the western North Pacific and China Seas was nearly normal and