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GEOGRAPHY AND CLIMATE
year when the weather is generally dry and sunny. After the New Year there is often more cloud and although rainfall remains slight it is often fairly persistent. Coastal fog and drizzle occur from time to time in early spring-during breaks in the monsoon-when warm south-easterly winds may temporarily displace the cool north- easterlies.
The summer monsoon blows from the south or south-west and can occur from mid-April until September, but it is not as persistent as the north-east monsoon of winter. Summer is the rainy season and is almost continuously hot and humid. The annual rainfall measured at the Royal Observatory has varied between 901.1 mm in 1963 and 3040.7 mm in 1889 but the mean value is 2168.8 mm.
The mean daily temperature ranges from about 15°C in February to about 28°C in July and the average for the year is 22°C. February is normally the coldest month and July the hottest. The absolute minimum and maximum temperatures ever recorded at the Royal Observatory were 0.0°C and 36.1°C respectively. However, greater extremes may occur in the New Territories where ice occasionally forms on high ground. Afternoon temperatures are usually about 5°C higher than those during the coldest part of the night. The mean relative humidity exceeds 80 per cent from mid-February until early September. November is the least humid month with a mean rela- tive humidity of 69 per cent, but the lowest reading of 10 per cent was recorded in January. The average daily duration of bright sunshine ranges from three hours in March to over seven hours in mid-July and late October.
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Gales caused by tropical cyclones may be expected in any of the months from May to November but they are most likely from July to September. The passage of these cyclones several times a year at varying distances from Hong Kong brings spells of bad weather with strong winds and heavy rain. Gales are experienced once a year on average, and less frequently the centre of a mature typhoon passes sufficiently close to the Colony to produce winds of hurricane force, endangering life and property.
THE ROYAL OBSERVATORY
The Royal Observatory is directly concerned with all matters relating to meteorology and geophysics. Weather forecasts and trop- ical cyclone warnings are prepared in the general forecasting office, while services for aviation are provided at the airport meteorological office.