A gloomy and warm November

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     As the northeast monsoon affecting the south China coast was relatively weak, southerlies dominated in the lower atmosphere and water vapour built up, causing Hong Kong's weather in November 2018 to be cloudier and gloomier than usual. The mean amount of cloud in the month was 79 per cent, 25 per cent above the normal figure of 54 per cent – the highest on record for November. The duration of bright sunshine in the month was only 123.9 hours, about 31 per cent lower than the normal figure of 180.1 hours and the eighth lowest on record for November. Despite the gloomy weather, the month was warmer than usual. The mean temperature of 22.9 degrees and mean minimum temperature of 21.4 degrees were 1.1 degrees and 1.6 degrees above the respective normal figures, and were the ninth and fourth highest on record for November. The month was also wetter than usual with 73.4 millimetres of rainfall, about 95 per cent above the normal figure of 37.6 millimetres. The accumulated rainfall up to November this year was 2151.0 millimetres, a deficit of about 9 per cent compared to the normal figure of 2371.7 millimetres for the same period.
 
     Tropical cyclone Yutu edged north slowly towards the coast of eastern Guangdong and weakened gradually on November 1 and 2. It eventually dissipated over the northeastern part of the South China Sea in the morning of November 3. Under the combined effect of the northeast monsoon and tropical cyclone Yutu, it was windy and dry with sunny periods in Hong Kong on the first day of November. While local winds subsided gradually, it was mainly cloudy with a few rain patches over the next two days.
 
     Affected by the northeast monsoon, the weather turned windy with a few light rain patches in Hong Kong on November 4. As the cloud band covering the coast of Guangdong dissipated gradually, the weather in Hong Kong became generally fine over the next three days. With a replenishment of the northeast monsoon arriving at the coastal areas of Guangdong in the morning of November 8, there were sunny periods with one or two light rain patches in Hong Kong. The weather turned cloudier and windier with light rain on November 9 and 10 as winds from the east strengthened. With the easterly airstream moderating gradually, there were sunny periods during the day on November 11 and 12. The temperature at the Hong Kong Observatory rose to a maximum of 28.0 degrees in the afternoon of November 12, the highest of the month. Under the influence of the northeast monsoon, winds strengthened on November 13, though the weather remained generally fine apart from a few light rain patches in the morning and at night.
 
     Under the influence of a fresh to strong easterly airstream, the weather in Hong Kong became mainly cloudy again with a few light rain patches from November 14 to 17. The weather improved with sunny periods during the day on November 18. With a replenishment of the northeast monsoon reaching the south China coastal areas, it was slightly cooler with sunny intervals on November 19 and 20.
 
     There were sunny periods during the day in Hong Kong on November 21. As a cold front moved across the coastal areas of Guangdong and winds from the north strengthened, the weather turned cloudy with a few rain patches at night. Affected by the northeast monsoon behind the cold front, the weather became appreciably cooler and drier, with sunny periods from November 22 to 24. With a broad rain-bearing cloud band covering southern China, local weather became cloudy and rainy from November 25 to 28. More than 20 millimetres of rainfall were recorded on November 25. Under the rain, the temperature at the Hong Kong Observatory dropped to a minimum of 17.0 degrees in the morning of November 26, the lowest of the month. With the cloud band thinning out gradually, sunshine returned on the last two days of the month.
 
     Four tropical cyclones occurred over the South China Sea and the western North Pacific in November 2018.
 
     Details of issuance and cancellation of various warnings/signals in November are summarised in Table 1. Monthly meteorological figures and departures from normal for November are tabulated in Table 2.

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