The Weather of May 1998

    May 1998 was warmer than usual. Both the mean temperature of 26.8 degrees and the mean minimum temperature of 25.0 degrees ranked the seventh highest for the month of May. The rainfall recorded in the month totalled 335.2 millimetres, six per cent above normal. However the accumulated rainfall since January amounted to 830.2 millimetres which was 35 per cent above the normal for this five-month period. The Red Rainstorm Warning Signal was issued twice during the month, on 2 and 24 May respectively.

    The weather on the first day of the month was mainly fine. As a trough of low pressure approached from the north, it turned cloudy the next day and squally thunderstorms together with heavy showers set in towards the evening. Altogether there were 16 reports of flooding and trees more than ten metres tall were reported to have fallen in Tsuen Wan, Fanling and Yuen Long during the deluge. Isolated thunderstorms continued in the next two days. As the trough moved away, fine and sunny weather returned on 5 May and lasted till 8 May.

    It was cloudy with isolated showers on 9 May. The weather turned fine and sunny the next day although there were some brief heavy showers early in the morning. Fine weather continued and temperatures rose to 32.2 degrees, the highest in the month, on 11 May. Apart from some isolated showers in the New Territories on 12 May, it remained generally fine to 14 May.

    As another trough of low pressure approached from the north, the weather turned cloudy again with occasional heavy showers and squally thunderstorms on 15 May. There were 12 cases of flooding reported in Kowloon and the New Territories. It became fine and sunny on 16 May as the trough moved to the northern part of the South China Sea. However showery conditions resumed the next day as the trough retreated northward closer to the coastal areas. While this trough lingered around the vicinity, the weather remained cloudy with occasional showers during the following week and there were isolated thunderstorms on 19 and 21 May.

    A cold front developed to the north of Hong Kong and moved south on 24 May bringing heavy showers and squally thunderstorms to local areas. The heaviest downpour took place near Sha Tau Kok where over 300 millimetres of rainfall were recorded in the morning and early afternoon. There were 37 cases of flooding and one landslip in the northern part of the New Territories. In addition, six more cases of flooding were reported in Yuen Long and another three in Tuen Mun. About 240 people marooned in floods were evacuated by helicopters and dinghies. Winds freshened from the north in the afternoon and became strong offshore in the evening as the rain let up. It was cloudy with a few isolated showers on 25 May and temperatures fell to 21.2 degrees, the lowest in the month. Winds moderated gradually in the day.

    It remained cloudy on 26 and 27 May but the weather became fine and sunny on 28 May. It was mainly fine the next day apart from some isolated showers in the evening.

    Under the influence of a fresh easterly airstream, cloudy weather with occasional heavy showers prevailed on the last two days of the month. Winds became strong offshore on the evening of 30 May and moderated during the day on 31 May.

    No tropical cyclone occurred in the western North Pacific and the South China Sea in the month. During the month, a total of 9 aircraft was diverted due to adverse weather.