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Deluge from a rainstorm late in the month made March 2004 wetter than usual. The monthly rainfall was 104.3 millimetres, about 56 per cent more than the normal figure of 66.9 millimetres. The accumulated rainfall since the beginning of the year is 207.1 millimetres, about 50 per cent above the normal figure of 138.3 millimetres for the same period.
Under the influence of a maritime airstream, March started off warm with sunny periods during the day. A cold front crossed the South China coast overnight on 2 March, bringing some rain and appreciably cooler weather to Hong Kong. The temperature fell to 13.3 degrees in the morning of 4 March, which was the lowest of the month. The sky cleared quickly that day as a dry northeast monsoon established over South China. It became warmer in the next eight days. With an abundance of sunshine, the maximum temperature rose to 26.2 degrees on 11 March, the highest in the month.
The fine spell came to an end as another cold front crossed the South China coast on 13 March, bringing with it some light rain. It became hazy as the northeast monsoon behind the cold front subsided on 14 March. While it remained cloudy in the next few days, mist set in as a moist maritime airstream affected Hong Kong on 17 March. Isolated thunderstorms drifted across Hong Kong that afternoon, necessitating the issuance of the first Thunderstorm Warning of the year.
Winds strengthened from the east on 18 March, bringing mist and light rain patches to the territory that afternoon. While it remained cloudy in the ensuing day, there were periods of bright sunshine on 20, 21 and 22 March as the easterlies moderated. Winds strengthened from the east again on 23 and 24 March and the weather turned cloudy with some light rain patches.
A rain bearing cold front crossed Hong Kong on 25 March. It became overcast with rain for the rest of the month. It was misty inside the harbour on 25, 28 and 29 March with visibility falling below 3000 metres. On 30 March an active trough of low pressure brought thunderstorms and heavy rain to Hong Kong. Some 70 millimetres of rain was recorded at the Hong Kong Observatory that evening and the first Amber Rainstorm Warning of the year was issued. Mist was reported in the last day of the month.
One tropical cyclone occurred in the western North Pacific in the month.
Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.5. Monthly meteorological figures and departures from normal for March are tabulated in Table 2.
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