With the relatively dry northeast monsoon affecting southern China for most of the month, the weather of October 2012 was drier than usual. The monthly total rainfall of 46.4 millimetres was only about 46 per cent of the normal figure of 100.9 millimetres. The accumulated rainfall since January 1 was 1,804.8 millimetres, a deficit of 23 per cent compared to the normal figure of 2,334.0 millimetres for the same period. The mean temperature of the month was 25.6 degrees, near the normal figure of 25.5 degrees.

     Affected by the northeast monsoon, the weather in Hong Kong was mainly fine and dry for the first four days of the month. A replenishment of the northeast monsoon reached the coast of Guangdong on the morning of October 5, bringing fresh easterly winds. Locally, apart from a few light rain patches in the morning, it was mainly fine and dry during the day from October 5 to 7. With the prevalence of a dry continental airstream, local weather remained generally fine and dry but with some haze for the ensuing eight days.

     A weak cold front formed over central China and moved towards the coastal areas gradually on October 16. The weather in Hong Kong turned mainly cloudy with light rain patches on that day. With the passage of the cold front across the coast of Guangdong, there was some haze locally on October 17 and the weather became slightly cooler on the morning of October 18. A ridge of high pressure established along southeastern China, bringing generally fine and dry weather to Hong Kong from October 19 to 25.

     Meanwhile, tropical cyclone Son-Tihn intensified into a tropical storm while crossing Luzon on October 24. It entered the South China Sea on October 25 and then tracked generally west-northwestward across the central part of the South China Sea in the next two days, intensifying to a severe typhoon on the evening of October 27. Over the south China coastal areas, the northeast monsoon continued to dominate. Under the combined effect of the northeast monsoon and Son-Tihn, it was windy with a few rain patches in Hong Kong on October 26 and 27. The weather improved with sunny periods on October 28, as Son-Tihn moved away and entered Bei Bu Wan as well as weakened gradually.

     After making landfall over the coast of northern Vietnam, Son-Tihn turned to drift eastwards on October 29, and finally dissipated over Bei Bu Wan the next day. While the rain-bearing cloud band associated with Son-Tihn spread eastwards, affecting the south China coast on these two days, the northeast monsoon continued to prevail over the region. In Hong Kong, it was cloudy and windy with rain and mist patches on October 29 and 30. The rain became persistent on October 30 with more than 40 millimetres of rainfall recorded over parts of the territory. Meanwhile, a cold front formed over inland Guangdong and moved southwards to reach the coast on the night of October 30. Affected by the intense northeast monsoon behind the cold front, it became significantly cooler in Hong Kong with temperatures dropping generally to below 20 degrees that night. The last morning of the month remained cloudy and cool with rain. The temperature at the Observatory fell to a minimum of 17.7 degrees on that day, the lowest of the month. With the arrival of the dry continental airstream, local weather became fine and dry in the afternoon.

     Six tropical cyclones occurred over the South China Sea and the western North Pacific in the month.

     Details of the issuance and cancellation of various warnings and signals in the month are summarised in Table 1. Monthly meteorological figures and departures from normal of October are tabulated in Table 2.

Ends/Friday, November 2, 2012
Issued at HKT 19:26

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