ENG-1989 — Page 386

THE ENVIRONMENT

flooding. At the airport, more than 100 flights were diverted, delayed or cancelled. Bus, tram and ferry services were all suspended.

In sharp contrast with the previous month, June was exceptionally dry. A total of only 137.5 millimetres of rainfall was recorded against a normal amount of 431.8 millimetres. This is the eighth lowest on record for June. The Strong Wind Signal No. 3 was on display during the approach of Typhoon Dot from June 9 to 10.

Although two tropical cyclones affected Hong Kong in July, the monthly rainfall amounted to only 237.9 millimetres, equivalent to about three quarters of the normal figure of 316.8 millimetres. Typhoon Gordon necessitated the hoisting of the No. 8 Gale or Storm Signal between July 17 and 18. It brought squally showers and abnormally high tides to the territory causing thirteen cases of flooding, mostly in the outlying islands and New Territories. The more severe cases occurred in Tai O where water level rose by more than one metre, and at Ping Ha Road in Yuen Long. During the passage of Gordon, local ferries, buses, trams and ferry services to China and Macau were suspended. At the international airport, 40 flights were delayed, 19 diverted, and 13 cancelled. A trough of low pressure moved southwards across Hong Kong on July 29. The cool air behind the trough caused a drop in temperature the next morning to 21.7°C, the lowest July temperature registered in Hong Kong since records began.

August was warmer and drier than usual. Although eight tropical cyclones occurred in the western North Pacific, none of them affected Hong Kong. The monthly rainfall amounted to only 218.0 millimetres which is about half the normal figure of 413.4 millimetres. The weather was rainy and thundery on August 20. Rain became more frequent and heavy later on August 22 and in Tai Po, an 11-year-old girl and 15-year-old boy were swept away by swift stream currents and later found dead. Ten minor floods were reported in the New Territories and eight in the urban areas. Two minor landslips also occurred, one in Diamond Hill and the other in Tsuen Wan.

On the whole, September was rather warm with the month's mean temperature of 28.1°C being the fourth highest on record for September and the mean minimum temperature, 26.0°C, being the fifth highest.

October was rather windy with the Strong Wind Signal No. 3 hoisted on three occasions and the Strong Monsoon Signal hoisted on four other occasions. Four typhoons traversed the northern part of the South China Sea during the month.

November weather was dominated by the Asiatic continental anticyclone and associated monsoon. As a result, the monthly mean atmospheric pressure of 1 019.7 hectopascals in Hong Kong was the fifth highest on record for November, and the Strong Monsoon Signal was hoisted on four occasions.

There was a sharp contrast between the weather in the first part of December and that in the latter. The first part was characterised by clear sky and brilliant sunshine while the latter was cloudy and rainy. Total rainfall for the month amounted to 40.2 millimetres which was 59 per cent above average for December.

Geophysical, Oceanographic and other Services

The Royal Observatory carries out geophysical and oceanographic studies to provide the technical details required by engineering consultants undertaking major civil or coastal development projects.

During the year, forecasts of waves and swells in Hong Kong waters continued to be made. Microprocessor-based data logging systems were fabricated to store tidal

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