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March 2012 was characterized by a distinctive transition from humid to dry weather. Resulting from the contests between the northeast monsoon and maritime airstream over the south China coastal areas, the weather of the first half of the month in Hong Kong was gloomier, cooler and more humid than usual. In contrast, the second half of the month was generally fine, mild and dry under the prevalence of a continental airstream for most of the time. Overall, the mean temperature and relative humidity of the whole month are both near-normal. The monthly rainfall was only 22.1 millimetres, about 27 percent of the normal.
Under the influence of a humid easterly airstream, the weather was cloudy with light rain patches and coastal fog on the first day in the month. With the clouds thinning out during the day, it was warm with sunny periods on 2 March. The northeast monsoon reached the coast of Guangdong on 3 March, bringing cloudy, foggy and slightly cooler weather to the territory on 3 and 4 March. While remaining foggy, the weather became warm in the following two days as a maritime airstream prevailed over the coastal areas. Affected by another northeast monsoon over southern China, local weather became cooler with fog and rain patches from 7 to 9 March. With the strengthening of the northeast monsoon, it turned cold amidst mist and rain patches for the ensuing four days. The minimum temperature at the Observatory dropped to 11.4 degrees on 12 March, the lowest of the month. With the northeast monsoon over southern China abating gradually, it was mainly cloudy with a few light rain patches on 14 and 15 March.
Affected by a humid and mild maritime airstream over the coastal areas of Guangdong, it was mainly fine but foggy in the morning from 16 to 18 March. The visibility in eastern Harbour and at Waglan Island once fell below 100 metres in the morning on 18 March. With plenty of sunshine, the temperature at the Observatory rose to a maximum of 28.8 degrees on the same day, the highest of the month.
The arrival of the northeast monsoon over the coast of Guangdong on the morning of 19 March brought some fog patches to Hong Kong. Affected by the associated fresh to strong easterly airstream, local weather was slightly cooler in the following three days.
A cold front moved across the coastal areas of Guangdong on 23 March. Under the influence of the associated intense northeast monsoon, local temperature fell significantly in the afternoon on 23 March and the weather became rather cool and dry the next day. With the persistence of the continental airstream, the weather was generally fine and dry with temperature rising from 25 to 28 March. It was warm with sunny periods on 29 and 30 March. A weak cold front moved across the coastal areas of Guangdong on the morning of 31 March and brought mainly cloudy weather to the territory.
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