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GEOGRAPHY AND CLIMATE
Rainfall had been below normal during the latter part of 1969 and the dry weather continued in early January 1970. There was some frost in the New Territories on January 20 but the month as a whole was not abnormally cold. February was exceptionally mild and in particular the Lunar New Year holiday was memorably fine and warm. An unseasonable typhoon, Nancy, which developed over the Pacific, was the first February typhoon on record to last for more than seven days.
March was cloudy and cool with long periods of drizzle. The total sunshine duration of 31.2 hours was the lowest recorded in any March since 1905. During April some rain was reported on 17 days but nevertheless the accumulated rainfall was the third lowest on record.
May was hot and very wet. It was the first month since the previous July in which the monthly rainfall exceeded the normal amount. A trough of low pressure moving backwards and forwards across south China caused a very rainy spell between May 10 and 15. There were numerous floods and landslides on May 13.
June was uncomfortably hot and humid. The mean wet bulb temperature, which has occasionally been used as the basis for a discomfort index, was 25.9°C, the highest ever recorded in any June. Rainfall was near normal. July was also a very hot month and the monthly mean temperature of 29.3°C was the second highest of any month on record. However the humidity was low. The mean relative humidity of 78 per cent was the third lowest on record for any July. There were two tropical cyclones in July. Typhoon Olga hit Japan on July 5. Tropical storm Ruby passed about 40 miles to the east of Hong Kong on July 16 and on the following day a maximum instantaneous rate of rainfall of 378 mm/h was recorded at the Royal Observatory. This is the highest rate ever recorded. The previous record of 320 mm/h occurred on August 3, 1955.
August was a fairly normal month. Six tropical cyclones developed: three affected Japan and Korea, one North Vietnam and two caused strong winds in Hong Kong. The tropical depression which passed north of Hong Kong on August 3 also caused severe thunderstorms and 223.5 mm of rain, whereas tropical storm Violet which passed Hong Kong early on August 9 was relatively dry.