ENG-1972 — Page 248

THE ENVIRONMENT

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heaviest falls occurred on May 10 and 11, when violent thunderstorms and squalls produced 325 mm of rain at the Royal Observatory. Maximum gust peak speeds during the squalls were 81 knots at the King's Park Meteorological Station and 75 knots at Tate's Cairn. The heavy rain caused landslides and widespread flooding, disrupting traffic in various parts of the territory. During the month, thunderstorms and heavy rain warnings were issued on 15 occasions.

Tropical Depression Mamie developed over the western part of the South China Sea on June 3. It moved across the Vietnam coast and dissipated overland the next day. On June 10, another tropical depression formed about 190 miles south of Hong Kong. It moved east north-eastwards and did not affect Hong Kong.

A very active trough of low pressure moved slowly southwards across South China on June 14 resulting in Hong Kong's weather deteriorating rapidly on June 15, the day of the Dragon Boat Festival. During the next three days, continuous heavy rain with frequent thunderstorms, reminiscent of the rainstorms of June 1966, were experienced and the maximum hourly rainfall of 98.7 mm recorded on June 18 was close to the record value of 108.2 mm set in 1966. It was the first time in the recorded history of the Royal Observatory that rainfall in excess of 200 mm fell in three con- secutive days. Thunderstorms and heavy rain warnings were issued and renewed almost continuously from June 15 to 18. During this period, widespread flooding and serious traffic disruption were reported in nearly all parts of Hong Kong, with the excessive rainfall resulting in the disastrous landslides at Sau Mau Ping and the col- lapse of several buildings at Kotewall Road/Po Shan Road on June 18.

Typhoon Ora formed over the western Pacific to the east of the Philippines on June 24. It moved north-westwards across the central Philippines and dissipated over the Luichow Peninsula on June 27.

In July, strong winds were experienced in Hong Kong during the passage of Typhoon Susan. The typhoon formed on July 7 over the South China Sea off Luzon, and drifted slowly north-westwards until it came to about 160 miles south-east of Hong Kong on July 9. It then began to move in a series of loops to the west of Pratas Island. During the following five days, Susan moved very slowly in a generally north- ward direction towards the South China coast east of Hong Kong and its closest approach was about 90 miles. The erratic movement of Susan necessitated the fre- quent hoisting and lowering of No 1 and No 3 signals which were displayed for a period of 140 hours from July 8 to 14. On July 14, Susan finally moved away steadily north-eastwards across the Taiwan Strait and degenerated into an area of low- pressure near the east coast of China. Since records began in 1884, Susan was the first tropical cyclone which has remained within 200 miles of Hong Kong for more than five days.

August was wet with rainfall about 50 per cent above normal. An active trough of low-pressure remained almost stationary along the South China coast from August 8 to 14 and caused unsettled weather with thunderstorms in Hong Kong.

Typhoon Betty developed over the western Pacific on August 8 and moved on a north-westerly course. It crossed the East China coast near Foochow on August 18