The Weather of June 1999

    With the persistence of a southerly airstream over the south China coast, June 1999 was the warmest June since records began in 1884 with a monthly mean temperature of 28.9 degrees. The mean maximum temperature of 31.5 degrees and the mean minimum temperature of 26.8 degrees were the third and the fifth highest respectively for the month. The monthly total rainfall of 197.4 millimetres was 178.6 millimetres below normal. The accumulated rainfall of 580.2 millimetres since 1 January was about 42 per cent below the normal figure. Furthermore, the mean relative humidity of 79 per cent was the third lowest for the month. The Increasing Gale or Storm Signal Number 9 was hoisted on 7 June during the passage of Typhoon Maggie.

    Apart from a few isolated showers, it was fine and hot the first four days of the month. Meanwhile a tropical depression named Maggie formed to the east of the Philippines gradually intensifying into a typhoon. As Maggie moved across the Bashi Channel into the South China Sea heading for Hong Kong, local weather turned hazy on 5 and 6 June. It was very hot on the afternoon of 6 June with the maximum temperature reaching 33.4 degrees, the highest in the month.

    On 7 June, Maggie swept across Hong Kong in the early hours. Many areas experienced gale or storm force winds. The weather became overcast with heavy showers. Winds moderated in the afternoon as Maggie moved westward to the coastal waters of western Guangdong and gradually weakened. However, its re-intensification and slow eastward movement in the evening brought strong winds to Hong Kong again. It made landfall the next morning before dissipating over inland Guangdong in the afternoon.

    Sunny weather returned on 9 June although there were still isolated showers. After a few isolated thunderstorms the next morning, generally fine and hot weather persisted till 14 June. It became cloudy with isolated showers the next couple of days.

    Under the influence of an unstable southerly airstream, isolated thunderstorms occurred on the morning of 17 June. Temperatures dropped to 25.0 degrees in thundery showers, the lowest in the month. There were again isolated thunderstorms the next day.

    A trough of low pressure formed over southern China crossed the coast early on 19 June bringing showers to local areas. Hong Kong came under the influence of an unstable southerly airstream again the next few days and there were occasional heavy thundery showers on 20 and 21 June. Over 80 millimetres of rainfall were recorded over the southwestern part of Hong Kong Island on the morning of 21 June. It remained cloudy with isolated thunderstorms on 22 June.

    Southwest monsoon brought strong winds and isolated thunderstorms to Hong Kong on 23 June. The monsoon gradually moderated in the evening but cloudy conditions persisted with isolated showers the next day. It turned fine and sunny on 25 June and fine weather prevailed for the rest of the month apart from some isolated showers.

    One tropical cyclone, Typhoon Maggie, occurred in the South China Sea and the western North Pacific in the month.

    During the month, a total of seven aircraft was diverted due to adverse weather.