ENG-1977 — Page 264

THE ENVIRONMENT

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about five can be expected to cause strong winds in Hong Kong and about one gale- force winds or higher. Tropical cyclones occur in the Pacific and the South China Sea throughout the entire year, although none has caused gales in Hong Kong between December and April. When a tropical cyclone is about 600 to 800 kilometres from Hong Kong, the weather is usually fine and very hot. As it moves closer, winds increase and rain becomes heavy and widespread. The severe weather associated with a tropical cyclone usually affects Hong Kong for one to three days.

Spring is characterised by cloudy skies, periods of light rain or drizzle and, occa- sionally, very humid conditions with coastal fog. Temperatures tend to fluctuate widely from day to day, but show a marked increase over the season. Autumn is usually sunny and dry and only occasionally interrupted by tropical cyclones or outbreaks of cold air, making it generally the best time for visiting Hong Kong.

The mean annual rainfall is 2,168.8 millimetres, of which about 80 per cent falls between May and September. The wettest month of the year is June, when rain occurs about two days out of three and the average monthly rainfall amounts to 401.2 mm. The driest month is December, when the monthly average is only 24.9 mm and when rain usually falls on only about five days in the month. Climatological informa- tion on Hong Kong's weather is given in Appendix 39.

The 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 occur most frequently between April and September. Waterspouts, hailstorms and snow are comparatively rare. Although the lowest temperature recorded at the 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's total rainfall of 1,680 millimetres represented only 77 per cent of the average value and was the lowest since 1967. Conditions were extremely dry during the first four months of the year and the rainfall for the five-month period ending March 31 amounted to only 29.2 mm-the lowest ever recorded for that period. During the prolonged drought, there were Press reports of heavy losses among farmers, flower growers and fish breeders. Large stretches of farm land in the New Territories were abandoned because of the lack of water as wells and streams dried up. The year as a whole was sunnier and warmer than usual. The year's mean tem- perature of 23.3°C ranked second highest on record, but was equalled in 1963 and 1973; the warmest year was 1966 with a mean temperature of 23.8°C. The summer was rather hot but not very humid. The annual mean atmospheric pressure of 1,013.5 millibars equalled the highest on record.

During the year, 21 tropical cyclones were reported over the western North Pacific and the South China Sea. Although tropical cyclone warning signals were displayed on eight occasions in Hong Kong, very little damage was reported. Severe Tropical Storm Freda, the only tropical cyclone for which gale or storm signals were hoisted, passed about 128 kilometres to the south-south-west of Hong Kong on September 24 and resulted in gale-force winds.