The Weather of May 2003

    May 2003 was slightly drier than usual. The monthly rainfall of 249.0 millimetres was about 79 per cent of the normal figure of 316.7 millimetres. The accumulated rainfall since the beginning of the year was 408.9 millimetres, about two-third of the normal figure of 616.5 millimetres for the same period.

    Under the influence of an easterly airstream, it was cloudy in the first 2 days of May 2003. An unstable maritime airstream set in on 3 May and brought 3 days of rainy weather to Hong Kong. The rain was heaviest in the small hours of 5 May when a trough of low pressure developed along the south China coast. The Red Rainstorm Warning and Landslip Warning were issued for the first time this year. There were 89 reports of flooding, most of them in the northern part of the New Territories. A senior police inspector died in a rescue mission in a flooding incident at Lin Ma Hang.

    The weather improved on 6 May when the trough of low pressure dissipated. There were sunny periods in the next 3 days. The northeast monsoon established itself over south China on 9 May, giving rise to a mixture of sunshine and showers for the following 8 days. It became overcast with thunderstorms on 18 May when an active trough of low pressure crossed the South China coast. The rain gradually eased off the next day and there were intervals of sunshine.

    The weather turned fine on 20 May. There were long periods of sunshine in the ensuing 4 days. A trough of low pressure crossed the south China coast on 25 May, bringing with it thunderstorms and heavy showers.

    On 26 May, a tropical depression over the South China Sea intensified into a tropical storm named Linfa. As a ridge of high pressure dominated over southeast China, Linfa did not have any effect on the local weather. Apart from some brief showers, it was mainly fine on 27 May. It became overcast in the next 2 days, and haze occurred on 29 May under light winds. The weather turned fine on 30 May but the hazy conditions continued. It was dry on the last day of the month with the relative humidity staying below 50 per cent during daytime.

    A total of 3 tropical cyclones occurred in the western North Pacific and the South China Sea in the month.

    Details of issuance and cancellation of various warnings/signals in the month are summarized in Table 1.1 to 1.3. Monthly meteorological figures and departures from normal of May are tabulated in Table 2.