Appendix F Meteorological Data

November 2018

November 2018 was much gloomier than usual. As the northeast monsoon affecting the south China coast was relatively weak and southerlies were dominated in the lower atmosphere, more water vapour was built up and the weather in Hong Kong was cloudier than usual. The mean amount of cloud in the month was 79 percent, 25 percent above the normal of 54 percent and the highest on record for November. As a result, the duration of bright sunshine in the month was only 123.9 hours, about 31 percent 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 normals and were respectively the ninth and fourth highest for November on record. November 2018 was also wetter than usual with the monthly rainfall of 73.4 millimetres, about 95 percent above the normal of 37.6 millimetres. The accumulated rainfall up to November this year was 2151.0 millimetres, a deficit of about 9 percent compared to the normal of 2371.7 millimetres for the same period.

December 2018

With the northeast monsoon over southern China weaker than normal for most of the time in the month, December 2018 was much warmer than usual in Hong Kong. The monthly mean temperature was 19.2 degrees, 1.3 degrees above the normal of 17.9 degrees and among the sixth highest on record for December. The mean minimum temperature was 17.6 degrees, 1.7 degrees above normal of 15.9 degrees and among the fourth highest on record for December. The month was also drier than usual with a total rainfall of 11.9 millimetres, only about 44 percent of the normal of 26.8 millimetres. The annual total rainfall of 2162.9 millimetres in 2018 was about 10 percent below the annual normal of 2398.5 millimetres.

January 2019

With relatively less cold air outbreaks from the north arriving at the south China coast in the month, January 2019 was much warmer than usual in Hong Kong. The monthly mean temperature of 18.1 degrees and monthly mean minimum temperature of 16.4 degrees were 1.8 degrees and 1.9 degrees above their corresponding normals and both were the third highest on record for January. The mean maximum temperature of 20.4 degrees was 1.8 degrees above the normal and the fifth highest on record for January. The month was also drier than usual with only 4.7 millimetres of rainfall recorded in the month, about one fifth of the normal of 24.7 millimetres for January.

February 2019

February 2019 was unseasonably warm in Hong Kong which was mainly attributed to weaker than normal northeast monsoon over the south China coast for most of the time in the month. The monthly mean temperature of 20.1 degrees, monthly mean minimum temperature of 18.4 degrees and monthly mean maximum temperature of 22.6 degrees were 3.3 degrees, 3.4 degrees and 3.7 degrees above their corresponding normals and all of them were the second highest on record for February. Together with the well above normal temperatures in December 2018 and January 2019, Hong Kong experienced the warmest winter on record from December 2018 to February 2019 with the winter mean temperature reaching 19.1 degrees, 2.1 degrees above the normal. Moreover, there were only 3 cold days this winter, the fewest on record. February 2019 was also wetter than usual. The monthly rainfall was 68.7 millimetres, about 26 percent above the normal of 54.4 millimetres in February. The accumulated rainfall recorded in the first two months of the year was 73.4 millimetres, a deficit of 7 percent compared to the normal of 78.9 millimetres for the same period.

March 2019

As the northeast monsoon over southern China was weaker than normal for most of the time in the month, March 2019 continued to be much warmer than usual in Hong Kong with a mean temperature of 21.0 degrees, 1.9 degree above the normal of 19.1 degrees and the fourth highest on record for March. The mean minimum temperature of the month was 19.4 degrees, 2.2 degrees above normal of 17.2 degrees and the third highest on record for March. Moreover, for the first quarter (January to March) of 2019, the mean temperature of 19.7, mean maximum temperature of 22.1 and mean minimum temperature of 18.1 were all the highest on record for the same period. Affected by troughs of low pressure over the coastal areas of Guangdong in the early part of the month, the weather of Hong Kong was also wetter than usual in March 2019. The total rainfall of 186.5 millimetres in the month was more than twice the normal of 82.2 millimetres. The accumulated rainfall recorded in the first three months of the year was 259.9 millimetres, nearly 61 percent above the normal figure of 161.3 millimetres for the same period.

April 2019

The exceptionally warm weather in the first quarter of 2019 continued in April 2019, mainly attributing to the warmer than normal sea surface temperature and stronger than usual southerly flow in the lower atmosphere over the northern part of the South China Sea. The mean minimum temperature of 22.9 degrees and mean temperature of 24.7 degrees were both 2.1 degrees above the corresponding normal and respectively one of the highest and second highest on record for April. The mean maximum temperature of 27.2 degrees was 2.2 degrees above the normal and the fifth highest on record for April. The monthly rainfall was 185.8 millimetres, about 6 percent above the normal of 174.7 millimetres. The accumulated rainfall recorded in the first four months of the year was 445.7 millimetres, about 33 percent above the normal figure of 336.1 millimetres for the same period.

May 2019

With more than usual moisture content in the lower atmosphere over southern China, May 2019 was gloomier than usual in Hong Kong. The mean amount of cloud in the month was 83 percent, 7 percent above the normal of 76 percent and the duration of bright sunshine in the month was only 83.1 hours, about 41 percent lower than the normal figure of 140.4 hours and the second lowest on record for May. With less sunshine and the prevalence of the cooler easterlies in the early part of the month, the month was cooler than normal with the monthly mean temperature of 25.3 degrees, 0.6 degree below the normal figure of 25.9 degrees. Overall, attributing to the well above normal temperatures in March and April, the spring of Hong Kong in 2019 was still much warmer than usual with the mean temperature from March to May 2019 reaching 23.7 degrees, 1.2 degrees above the normal and one of the fifth highest on record for the same period. The monthly rainfall was 234.6 millimetres, about 23 percent below the normal of 304.7 millimetres. The accumulated rainfall recorded in the first five months of the year was 680.3 millimetres, about 6 percent above the normal figure of 640.8 millimetres for the same period.

June 2019

Mainly attributing to the warmer than normal sea surface temperature and stronger than usual southerly flow in the lower atmosphere over the northern part of the South China Sea, June 2019 was much hotter than usual in Hong Kong. The monthly mean temperature of 29.0 degrees was 1.1 degree above the normal figure of 27.9 degrees, one of the third highest on record for June. Moreover, the first half of this year from January to June 2019 was exceptionally warm. The mean temperature of 23.0 degrees, mean minimum temperature of 21.3 degrees and mean maximum temperature of 25.4 degrees were all the highest on record for the same period. The monthly rainfall of June 2019 was 429.1 millimetres, about 6 percent below the normal of 456.1 millimetres. The accumulated rainfall recorded in the first six months of the year was 1109.4 millimetres, slightly higher than the normal figure of 1096.9 millimetres for the same period.

July 2019

July 2019 was much hotter than usual in Hong Kong, mainly attributing to the warmer than normal sea surface temperature over the northern part of the South China Sea. The monthly mean minimum temperature of 27.7 degrees was 0.9 degree above the normal figure of 26.8 degrees, the highest on record for July. The monthly mean temperature of 29.5 degrees was 0.7 degree above the normal figure of 28.8 degrees, one of the sixth highest on record for July. The month was also cloudier than usual with the mean amount of cloud of 79%, about 10% above the normal figure of 69% and one of the fifth highest on record for July. The duration of bright sunshine in the month was only 150.5 hours, about 29% below the normal figure of 212.0 hours and the seventh lowest on record for July. The monthly rainfall was 328.5 millimetres, about 13 percent below the normal of 376.5 millimetres. The accumulated rainfall recorded in the first seven months of the year was 1437.9 millimetres, slightly lower than the normal figure of 1473.3 millimetres for the same period.

August 2019

August 2019 was hotter than usual in Hong Kong, mainly attributing to the warmer than normal sea surface temperature over the northern part of the South China Sea. The monthly mean temperature of 29.0 degrees was 0.4 degree above the normal figure of 28.6 degrees. Moreover, the summer of this year from June to August was exceptionally hot. The mean minimum temperature of 27.2 degrees, mean temperature of 29.2 degrees and mean maximum temperature of 31.8 degrees were respectively the second, third and fourth highest on record for the same period. Due to the heavy rain brought by tropical cyclones Wipha and Bailu, the month was wetter than normal with the monthly total rainfall amounting to 596.4 millimetres, about 38 percent above the normal figure of 432.2 millimetres. The accumulated rainfall recorded in the first eight months of the year was 2034.3 millimetres, a surplus of 7 percent compared to the normal of 1905.5 millimetres for the same period.

September 2019

With the dominance of upper-air anticyclone over southern China for most of the time in the month, Hong Kong experienced a hot, sunny and dry September in 2019. The monthly mean temperature was 28.7 degrees, 1.0 degree above the normal figure of 27.7 degrees and the seventh highest on record for September. There were seven consecutive hot nights from 8 to 14 September, the longest on record for September. Moreover, up to September, the annual number of hot nights in 2019 already reached 45, which is 27.2 days above the annual normal and the highest on record since 1884. September 2019 was marked by sunny weather with the monthly total sunshine duration amounting to 216.3 hours, about 26 percent above the normal of 172.3 hours. The month was also drier than usual with a total rainfall of 198.9 millimetres, about 61 percent of the normal figure of 327.6 millimetres. The accumulated rainfall this year up to September was 2233.2 millimetres, on par with the normal figure of 2233.1 millimetres for the same period.

October 2019

Owing to the stronger than normal upper-air anticyclone over southern China, October 2019 was exceptionally hot and sunny in Hong Kong. The monthly mean maximum temperature of 29.5 degrees, 1.7 degrees above the normal figure of 27.8 degrees, was the highest on record for October. The monthly mean temperature was 26.6 degrees, 1.1 degrees above the normal figure of 25.5 degrees and the second highest on record for October. The month was marked by sunny weather with the monthly total sunshine duration amounting to 230.7 hours, about 19 percent above the normal of 193.9 hours. With two heavy rain episodes respectively on 6 – 7 October and 13 – 14 October, the month was also wetter than normal with a monthly rainfall of 149.5 millimetres, about 48 percent above the normal of 100.9 millimetres. The accumulated rainfall this year up to October was 2382.7 millimetres, about 2 percent higher than the normal figure of 2334.0 millimetres for the same period.