ENG-1988 — Page 380

THE ENVIRONMENT

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falls between May and September. The wettest month is June, when rain occurs about two days out of three and the average monthly rainfall at the Royal Observatory is 431.8 millimetres. The driest month is December, when the monthly average is only 25.3 millimetres and rain falls on only about five days in the month.

Severe weather phenomena that can affect Hong Kong include tropical cyclones, strong winter monsoon winds, and thunderstorms with associated squalls that are most frequent from April to September. Waterspouts and hailstorms occur infrequently, while snow and tornadoes are rare. Climatological data are given in Appendix 45.

The Year's Weather

Total rainfall in 1988 was 1 685 millimetres, 24 per cent below the normal of 2 224.7 millimetres. The year's mean temperature of 22.8°C and mean relative humidity of 78 per cent were both normal.

January was warm with little rainfall. The mean temperature of 17.9°C was 2.3°C above normal and the mean minimum temperature of 16.1°C was 2.9°C above normal. Both were the second highest on record for January. Although rain was recorded on 13 days, the total rainfall amounted to only 1.0 millimetre.

For most of February, there were cloudy skies. The mean cloud amount of 81 per cent was 10 per cent above normal for the month. However, the total rainfall was only 11.9 millimetres.

March was a rather cool and cloudy month, and the mean temperature of 16.8°C was 1.7°C below normal. Under the influence of a warm and moist airstream from the Pacific, mist and fog developed on March 12, limiting visibility at Waglan Island to 100 metres throughout the day. Foggy conditions prevailed from March 12 to 15. In these conditions, two mishaps involving small vessels and resulting in injuries to some persons were reported. It was cooler and also drier than usual in April, with a mean relative humidity of 78 per cent, the third lowest on record for April. A total of 17 hill fires occurred in the sunny and dry conditions of April 24.

May was cloudier than normal. Although rainfall was recorded on 26 days, the total amount for the whole month was only 115.2 millimetres, 61 per cent below normal. On May 31, due to the approach of Typhoon Susan, the Stand By Signal No. 1 was hoisted for the first time during the year.

In June, total rainfall amounted to only 296.9 millimetres, 31 per cent below normal. For the first half of 1988, a total of 548 millimetres of rain fell, the fourth lowest on record for the period. June was also drier and warmer than normal. The mean relative humidity of 78 per cent was, like in June 1967, the lowest on record for the month. The mean temperature of 28.6°C was the fourth highest on record for June. Due to the approach of an active trough of low pressure, thunderstorms and heavy showers affected Hong Kong from June 23 to 27. Subsidence of the ground on June 24 made it necessary for 25 residents in Shau Kei Wan to be evacuated from their huts. The Stand By Signal No. I was again on display from June 28 to 29, due to the approach of Tropical Storm Vanessa. Antecedent rain and heavy showers on June 30 caused a minor landslip in Kwai Chung where 27 residents had to be evacuated.

July was the first month of the year with monthly rainfall slightly above normal. Most of the rainfall during the month was attributable to Typhoon Warren, which required the hoisting of the Strong Wind Signal No. 3 for the first time this year. Almost 250 millimetres of rainfall were recorded at the Royal Observatory during July 19 and 20 and over 300 millimetres fell in parts of the north-west New Territories, where widespread severe flooding occurred. A total of 270 hectares of agricultural land was flooded. Sixty-five