Appendix F Meteorological
Data
November
2020
With the northeast monsoon over southern China
generally weaker than normal for most of the time in the month, November 2020
was much warmer than usual in Hong Kong. The monthly mean maximum temperature
was 26.4 degrees, 2.3 degrees above the normal figure and the highest on record
for November. The monthly mean temperature of 23.5 degrees and mean minimum
temperature of 21.7 degrees were respectively 1.7 degrees and 1.9 degrees above
their corresponding normal figures and both were the second highest on record
for November. Moreover, the autumn mean temperature in Hong Kong for the period
from September to November 2020 was 25.8 degrees, 0.8 degrees above the normal
figure and one of the fourth warmest autumns on record. The month was also
drier than usual with a total rainfall of 5.1 millimetres, about 14 percent of the normal figure of 37.6 millimetres. The
accumulated rainfall this year up to November was 2393.5 millimetres, slightly
more than the normal figure of 2371.7 millimetres for the same period.
December
2020
The weather for December 2020 was cloudier than
usual. The mean amount of cloud in the month was 62 percent, 10 percent above
the normal of 52 percent. The mean temperature for December 2020 was 18.1
degrees, 0.2 degrees above the normal figure of 17.9 degrees. The month was
also much drier than usual with a total rainfall of only 1.5 millimetres, about
6 percent of the normal figure of 26.8 millimetres. The annual total rainfall
in 2020 was 2395.0 millimetres, near the annual normal of 2398.5 millimetres.
January 2021
January 2021 was characterized by colder weather
during the first half of the month and relatively milder weather in the latter
part. Overall, the month was colder than usual with a mean temperature of 16.2
degrees, 0.3 degrees below the normal figure of 16.5 degrees (or 0.1 degrees
below the 1981-2010 normal). With dry winter monsoon dominating over southern
China for most of the time in the month, January 2021 was also much sunnier and
drier than usual. The monthly total sunshine duration amounted to 217.3 hours,
49 percent above the normal of 145.8 hours (or 52 percent above the 1981-2010
normal). Only traces of rainfall was recorded in the month, making it one of
the eight Januaries with traces of rainfall since records began in 1884.
February
2021
With the northeast monsoon over southern China
generally weaker than normal for most of the time in the month, February 2021
was much warmer and sunnier than usual in Hong Kong. The monthly mean maximum
temperature of 23.5 degrees, monthly mean temperature of 19.8 degrees and
monthly mean minimum temperature of 17.5 degrees were 4.1 degrees, 2.7 degrees
and 2.2 degrees above their corresponding normals (or 4.6 degrees, 3.0 degrees
and 2.5 degrees above their corresponding 1981-2010 normals) and respectively
the second, third and fourth highest on record for February. The total duration
of bright sunshine in the month was 205.1 hours, more than twice of the normal
of 101.7 hours (or 110.9 hours above the 1981-2010 normal of 94.2 hours) and
the fourth highest on record for February. Mainly attributing to the
exceptional warm and sunny weather in February 2021, the winter from December
2020 to February 2021 was warmer than usual in Hong Kong. The mean temperature
of 18.0 degrees was one of the seventh highest on record for the same period.
The monthly rainfall was 62.1 millimetres, about 60 percent above the normal of
38.9 millimetres (or 14 percent above the 1981-2010 normal of 54.4 millimetres)
in February. The accumulated rainfall recorded in the first two months of the
year was 62.1 millimetres, a deficit of 14 percent compared to the normal of
71.9 millimetres (or 21 percent below the 1981-2010 normal of 78.9 millimetres)
for the same period.
March 2021
With relatively less cold air outbreaks from the
north, March 2021 continued to be exceptionally warm in Hong Kong. The monthly
mean maximum temperature of 24.8 degrees, monthly mean temperature of 22.0
degrees and monthly mean minimum temperature of 20.2 degrees were 2.9 degrees,
2.5 degrees and 2.6 degrees above their corresponding normals (or 3.4 degrees,
2.9 degrees and 3.0 degrees above their corresponding 1981-2010 normals) and
all of them were the highest of the correspondingly monthly mean values of
March on record. The month was also much drier than usual with a total rainfall
of only 3.5 millimetres, about 5 percent of the normal figure of 75.3
millimetres (or 4 percent of the 1981-2010 normal of 82.2 millimetres) and the
fourth lowest on record for March. The accumulated rainfall recorded in the
first three months of the year was 65.6 millimetres, a deficit of 55 percent
compared to the normal of 147.4 millimetres (or 59 percent below the 1981-2010
normal of 161.3 millimetres) for the same period.
April 2021
With relatively less cold air intrusion from the
north, April 2021 continued to be much warmer than usual in Hong Kong. The
monthly mean minimum temperature of 22.4 degrees, monthly mean maximum
temperature of 27.0 degrees and monthly mean temperature of 24.1 degrees were
1.3 degrees, 1.4 degrees and 1.1 degrees above their corresponding normals (or
1.6 degrees, 2.0 degrees and 1.5 degrees above their corresponding 1981-2010
normals) and respectively the fifth, seventh and ninth highest on record for
April. With the dominance of upper-air anticyclone over southern China for most
of the time in the month, April 2021 was also much drier than usual with a
total rainfall of only 32.5 millimetres, about 21 percent of the normal figure
of 153.0 millimetres (or 19 percent of the 1981-2010 normal of 174.7
millimetres). The accumulated rainfall recorded in the first four months of the
year was 98.1 millimetres, a deficit of 67 percent when compared to the normal
of 300.4 millimetres (or 71 percent below the 1981-2010 normal of 336.1
millimetres) and the tenth lowest on record for the same period.
May 2021
Mainly attributing to the stronger than usual
subtropical ridge over southern China, May 2021 was the hottest May in Hong
Kong on record. The monthly mean temperature of 29.0 degrees and monthly mean
minimum temperature of 27.0 degrees were 2.7 degrees and 2.5 degrees above
their corresponding normals (or 3.1 degree and 2.9 degrees above their
corresponding 1981-2010 normals) and both were the highest on record for May.
The mean maximum temperature of 32.1 degrees was 3.3 degrees above normal (or
3.7 degrees above the 1981-2010 normals) and the second highest on record for
May. Together with the exceptionally warm weather in March and April 2021, Hong
Kong experienced the warmest spring on record from March to May 2021. The mean
temperature of 25.0 degrees, mean minimum temperature of 23.2 degrees and mean
maximum temperature of 28.0 degrees for March to May 2021 were all the highest
on record for the same period. There were in total 14 hot nights in the month
including 6 consecutive hot nights that started from 16 May, both breaking the
records for May. The month was also much drier than usual with a total rainfall
of only 65.0 millimetres, about 22 percent of the normal figure of 290.6
millimetres (or 21 percent of the 1981-2010 normal of 304.7 millimetres). The
accumulated rainfall recorded in the first five months of the year was 163.1
millimetres, a deficit of 72 percent when compared to the normal of 590.9 millimetres
(or 75 percent below the 1981-2010 normal of 640.8 millimetres) and the second
lowest on record for the same period.
June 2021
June 2021 was marked by the long awaited rainy
weather brought by tropical cyclone Koguma, troughs of low pressure and the active
southwesterly airstream. The monthly rainfall of June 2021 was 628.0
millimetres, about 28 percent above the normal of 491.5 millimetres (or 38
percent above the 1981-2010 normal of 456.1 millimetres). The abundant rainfall
in the month alleviated the very dry condition of Hong Kong in the last few
months. The accumulated rainfall recorded in the first half of the year was
791.1 millimetres, a deficit of 27 percent compared to the normal of 1082.5
millimetres (or 28 percent below the 1981-2010 normal of 1096.9 millimetres).
The month was also warmer than usual with a mean temperature of 28.8 degrees,
0.5 degrees above the normal figure of 28.3 degrees (or 0.9 degrees above the
1981-2010 normals). Mainly attributing to the well above normal temperatures in
the previous four months, the first half of this year from January to June 2021
was exceptionally warm. The mean maximum temperature of 26.3 degrees, mean
temperature of 23.3 degrees and mean minimum temperature of 21.3 degrees were
all the highest on record for the same period.
July 2021
Owing to the stronger than normal upper-air
anticyclone over southern China, July 2021 was unusually hot in Hong Kong. The
monthly mean minimum temperature of 27.7 degrees, monthly mean maximum
temperature of 32.6 degrees and monthly mean temperature of 29.7 degrees were
0.8 degrees, 1.0 degree and 0.8 degrees above their corresponding normals (or
0.9 degrees, 1.2 degrees and 0.9 degrees above their corresponding 1981-2010
normals) and respectively the second, third and fourth highest on record for
July. The monthly rainfall was 379.5 millimetres, slightly below the normal
figure of 385.8 millimetres (or slightly above the 1981-2010 normal of 376.5
millimetres). The accumulated rainfall recorded in the first seven months of
the year was 1170.6 millimetres, about 20 percent below the normal figure of
1468.2 millimetres (or 21 percent below the 1981-2010 normal of 1473.3
millimetres) for the same period.
August 2021
August 2021 was characterized by cloudier than
usual weather with localized heavy rain over parts of the New Territories. The
mean amount of cloud in the month was 77 percent, 7 percent above the normal of
70 percent. As for monthly rainfall, while over 600 millimetres of rainfall
were recorded in parts of the North District of the New Territories, the
monthly rainfall recorded at the Observatory was 350.5 millimetres, about 23
percent below the normal figure of 453.2 millimetres (or 19 percent below the
1981-2010 normal of 432.2 millimetres). The accumulated rainfall recorded in the
first eight months of the year was 1521.1 millimetres, about 21 percent below
the normal figure of 1921.5 millimetres (or 20 percent below the 1981-2010
normal of 1905.5 millimetres) for the same period. The monthly mean temperature
of 28.8 degrees was near the normal figure of 28.7 degrees (or 0.2 degrees
above the 1981-2010 normal). Mainly attributing to the exceptionally hot
weather in July 2021, the summer of this year from June to August was much
hotter than usual. The mean temperature of 29.1 degrees was the sixth highest
on record for the same period.
September
2021
Mainly attributing to the stronger than usual
subtropical ridge over southern China, September 2021 was the hottest September
in Hong Kong on record. The monthly mean maximum temperature of 32.8 degrees,
monthly mean temperature of 29.7 degrees and monthly mean minimum temperature
of 27.8 degrees were 2.3 degrees, 1.8 degrees and 1.7 degrees above their
corresponding normals (or 2.7 degrees, 2.0 degrees and 2.0 degrees above their
corresponding 1981-2010 normals) and all of them were the highest on record for
September. There were in total 15 very hot days and 11 hot nights in the month,
both breaking the records for September. Moreover, from January to September,
the numbers of very hot days and hot nights so far in 2021 already reached 53
days and 57 days respectively, both breaking the previous records set in 2020.
September 2021 was also much drier than usual with a total rainfall of 129.6
millimetres, about 40 percent of the normal figure of 321.4 millimetres (or 40
percent of the 1981-2010 normal of 327.6 millimetres). The accumulated rainfall
up to September this year was 1650.7 millimetres, a deficit of 26 percent
compared with the normal of 2242.8 millimetres (or 26 percent below the
1981-2010 normal of 2233.1 millimetres) for the same period.