214
THE ENVIRONMENT
Heavy rainfall from tropical cyclones often causes more damage and casualties than the wind.
Spring is characterised by cloudy skies, periods of light rain or drizzle and some- times 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, generally making it the best time of year for visiting Hong Kong.
The mean annual rainfall is 2,246.4 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 457.5 mm. The driest month is December when the monthly average is only 25.9 mm and rain usually only falls on about five days in the month. October is the sunniest month when an average of 58 per cent of possible hours of sunshine are recorded. Climato- logical information on Hong Kong's weather is given in Appendix 39.
Severe weather phenomena that can affect Hong Kong include tropical cyclones mostly 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 from April to September. Waterspouts, hailstorms 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 total rainfall in 1978 was 2,593 millimetres or 15 per cent above the annual average. Substantial rain in March and April greatly eased the water situation in Hong Kong and a 24-hour supply was resumed on April 18, ending the restrictions imposed on June 1, 1977. By the end of April, rainfall was 63 per cent above normal. Although June and August were fairly dry, exceptionally heavy rain associated with Severe Tropical Storm Agnes in July and Severe Tropical Storm Nina in October made up the deficit. This brought the May to October rainfall up to 2,102 mm which is in the range predicted by the Royal Observatory.
Due to cloudy conditions between February and May, the year as a whole was cloudier and less sunny than usual. The total duration of sunshine in the year was 244 hours less than average and ranked as the eighth lowest on record. Mean temperatures in the year were near normal but the summer months were very hot.
Three new records were established in 1978 the total duration of sunshine in March was only 21.7 hours; maximum temperatures exceeded 33°C on 19 consecutive days during July and the temperature dropped to a minimum of 13.5°C in October. The 33 tropical cyclones reported over the western North Pacific and the South China Sea in 1978 caused heavy losses both in human life and property in many Asian countries, especially in the Philippines. Hong Kong suffered little damage from the eight tropical cyclones that approached during the year. The most serious was Severe Tropical Storm Agnes. Agnes is unique in that it is the only tropical cyclone for which gale signals were hoisted on two separate occasions. It was also the fourth wettest tropical cyclone since 1884. During its two approaches to Hong Kong, the Royal Observatory recorded a total of 519 mm of rain. Although no heavy damage to