The Weather of August 1998

    August 1998 was a very hot month. Both the mean temperature of 29.5 degrees and the mean minimum temperature of 27.4 degrees, which were the same as those recorded in August 1990, were the highest on record for August. In addition, the mean maximum temperature of 32.1 degrees was the second highest for August. On the other hand, the mean relative humidity, 79 per cent, was the eighth lowest for the month. With fewer than usual tropical cyclone activities in the South China Sea, the mean pressure of the month reached 1008.3 hectopascals, which was the third highest for August. A total of two tropical cyclones necessitated the hoisting of Tropical Cyclone Warning Signals. The first signal of the year was hoisted on 9 August, the latest date for hoisting this signal in post-war years.

    Despite having to issue the Amber Rainstorm Warning Signal on three occasions, the total rainfall of 245.4 millimetres in the month was 146 millimetres below normal. However the cumulative rainfall since 1 January, 2157.3 millimetres, was still 26 per cent more than the normal for the same period.

    The fine and clear weather at the end of July continued into August. Apart from one or two isolated showers, it was fine, sunny and very hot during the first few days of the month. Temperatures rose to 34.4 degrees, the highest in the month, on 3 August. The temperatures at Ta Kwu Ling was even higher, reaching a maximum of 37.2 degrees the following day.

    Thundery showers developed over the eastern part of the territory on 6 August and became widespread the next day. Although it became fine and sunny on 8 August, isolated heavy showers returned the next day with the approach of Tropical Storm Penny. During the next couple of days, rainbands associated with Penny brought frequent and heavy squally showers to the territory. Temperatures dropped to 24.8 degrees, the lowest in the month, in heavy showers on 11 August.

    After the dissipation of Penny, south China coastal areas came under the influence of a ridge of high pressure. The weather improved significantly and 12 August saw long sunny periods. The fine and sunny spell prevailed till 21 August, broken only on 18 August by thunderstorms in which one person in Tin Shui Wai was struck by lightning.

    Under the influence of a tropical depression formed over the northern part of the South China Sea, weather became thundery on 22 August. Showery weather continued the next day but it turned fine and sunny again on 24 August.

    Thunderstorms and heavy showers returned on the afternoon of 25 August. This unsettled weather persisted until the end of the month as Hong Kong gradually came under the influence of a trough of low pressure. On the evening of 30 August, the 400 000-kilowatt cable between Tai Po and Yuen Long was struck by lightning and power supply in Tai Po, Sai Kung, Tsuen Wan and eastern Kowloon was disrupted. A waterspout was reported over the Zhujiang Estuary about 20 kilometres northwest of Chek Lap Kok on the afternoon of 31 August.

    Four tropical cyclones occurred in the South China Sea and the western North Pacific in the month.

    During the month, no aircraft was diverted due to adverse weather.