The Year's Weather - 2009
According to the World Meteorological Organization, the year 2009 would likely rank among the top 10 hottest years globally on record. In Hong Kong, the weather was also exceptionally warm in 2009 with an annual mean temperature of 23.5 degrees, ranking the 9th highest on record with 1991 and 2006 (see Table 1). The average temperature in February reached a record high of 20.5 degrees, 4.2 degrees above the climatological normal. Also, prolonged hot weather extended from summer into late September, with altogether 30 days having daily maximum temperatures of 33 degrees or above, the highest since 1963. The Very Hot Weather Warning was in effect for a total of 40 days, the highest number since the warning started operation in 2000. The year 2009 was also drier than usual. The annual rainfall of 2182.3 millimetres was about 8 percent below normal.
A total of 30 tropical cyclones occurred over the western North Pacific and the South China Sea in 2009. Five tropical cyclones attained super typhoon intensity (maximum 10-minute wind speed of 185 km/h or above near the centre) over the western North Pacific. However, none of these directly affected Hong Kong. Eight tropical cyclones necessitated the issuance of local tropical cyclone warning signals this year, slightly more than the annual average of six to seven. Typhoon Molave passed about 40 km north-northeast of the Hong Kong Observatory Headquarters in July and necessitated issuance of the Increasing Gale or Storm Signal No. 9, the highest signal issued in the year. Two other tropical cyclones necessitated the issuing of the Gale or Storm Signal No. 8, namely Severe Tropical Storm Goni in August and Typhoon Koppu in September.
As for individual months, January 2009 was sunnier and drier than usual. The total bright sunshine duration for the month was 226.5 hours, about 60 percent above the normal.
Due to a lack of northerly surges, it was unusually warm in February. The month was the warmest February since records began in 1884. The temperature of 28.3 degrees recorded on 25 February was the highest ever on record for February. The month was also sunnier than normal.
March was wetter and warmer than usual.
The weather in April, May and June was drier than normal.
July was warmer than usual.
Under the influence of a stronger than normal sub-tropical ridge, the weather was much hotter than usual in August, September and October. The mean temperatures of 29.4 degrees for August, 28.8 degrees for September and 26.2 degrees for October were 1.0, 1.2 and 0.9 degrees higher than their respective climatological normals. The mean minimum temperatures of 27.7 degrees for August and 26.9 degrees for September were the highest for the respective months on record. It was also wetter than usual in September. The total rainfall of 486.3 millimetres in the month was about 69 percent above the normal.
The weather was cooler than usual in November. The temperature fell to 10.5 degrees on 17 November, the earliest day for winter since 1981 when the minimum temperature was 12.0 degrees or below. The first Cold Weather Warning issued on 16 November was also the earliest for winter since the warning started operation in 1999.
December was cooler and wetter than usual.
Figure 1 shows the monthly mean temperature in 2009 in comparison with the climatological normal values.
|
Year |
Annual mean temperature |
|
1998 |
24.0 |
|
2002 |
23.9 |
|
1999 |
23.8 |
|
1966 |
23.8 |
|
2007 |
23.7 |
|
2003 |
23.6 |
|
2001 |
23.6 |
|
1994 |
23.6 |
|
2009 |
23.5 |
|
2006 |
23.5 |
|
1991 |
23.5 |
 Month |
Mean Pressure (hPa) |
Air Temperature | Mean Dew Point (deg. C) |
Mean Relative Humidity (%) |
Mean Amount of Cloud (%) |
Total Rainfall (mm) |
||
|---|---|---|---|---|---|---|---|---|
Mean Daily Maximum (deg. C) |
Mean (deg. C) |
Mean Daily Minimum (deg. C) |
||||||
| January | 1021.9 | 18.3 | 15.3 | 13.0 | 8.1 | 64 | 40 | Trace |
| February | 1015.5 | 23.7 | 20.5 | 18.6 | 17.1 | 81 | 64 | 1.1 |
| March | 1015.2 | 22.1 | 19.7 | 17.9 | 16.6 | 83 | 81 | 120.7 |
| April | 1012.7 | 24.8 | 22.0 | 20.2 | 17.6 | 77 | 79 | 108.7 |
| May | 1010.8 | 28.8 | 25.5 | 23.5 | 21.2 | 78 | 70 | 245.2 |
| June | 1004.8 | 30.7 | 28.1 | 26.2 | 24.6 | 81 | 76 | 341.8 |
| July | 1005.1 | 31.9 | 29.1 | 27.0 | 25.3 | 81 | 69 | 389.4 |
| August | 1004.9 | 32.2 | 29.4 | 27.7 | 25.5 | 80 | 69 | 334.1 |
| September | 1007.5 | 31.9 | 28.8 | 26.9 | 24.6 | 78 | 66 | 486.3 |
| October | 1012.4 | 28.9 | 26.2 | 24.3 | 20.8 | 73 | 59 | 44.4 |
| November | 1017.7 | 23.2 | 20.5 | 18.3 | 15.1 | 72 | 61 | 60.4 |
| December | 1019.3 | 19.3 | 17.3 | 15.6 | 13.3 | 78 | 65 | 50.2 |
| mean or total | 1012.3 | 26.3 | 23.5 | 21.6 | 19.2 | 77 | 67 | 2182.3 |
| Normal* | 1013.0 | 25.6 | 23.1 | 21.1 | 18.8 | 78 | 67 | 2382.7 |
| Station | Hong Kong Observatory | |||||||
Month |
Number of hours of Reduced Visibility# (hours) |
Total Bright Sunshine (hours) |
Mean Daily Global Solar Radiation (MJ/m2) |
Total Evaporation (mm) |
Prevailing Wind Direction (degrees) |
Mean Wind Speed (km/h) |
|---|---|---|---|---|---|---|
| January | 251 | 226.5 | 14.13 | 91.4 | 360 | 25.9 |
| February | 137 | 140.7 | 12.70 | 74.2 | 070 | 21.0 |
| March | 133 | 70.1 | 9.23 | 69.6 | 070 | 23.8 |
| April | 148 | 119.3 | 13.63 | 100.1 | 070 | 28.9 |
| May | 17 | 169.8 | 17.00 | 124.5 | 080 | 22.0 |
| June | 8 | 127.1 | 14.06 | 118.5 | 220 | 18.4 |
| July | 5 | 197.4 | 19.30 | (155.0) | 100 | 21.5 |
| August | 81 | 192.1 | 16.52 | 136.5 | 230 | 16.1 |
| September | 49 | 181.3 | 15.64 | 145.0 | 080 | 28.4 |
| October | 248 | 202.6 | 14.74 | 120.2 | 080 | 23.0 |
| November | 141 | 171.4 | 12.75 | 97.6 | 360 | 25.5 |
| December | 266 | 124.5 | 9.15 | 60.1 | 010 | 25.8 |
| mean or total | 1484 | 1922.8 | 14.07 | 1292.7 | 080 | 23.3 |
| Normal* | 1452.3 § | 1842.9 | 13.23 | 1343.4 | 070 | 23.9 |
| Station | Hong Kong International Aiport |
King's Park | Waglan Island^ | |||
The minimum pressure recorded at the Hong Kong Observatory was 985.6 hectopascals at 0152 HKT on 19 July. The maximum air temperature recorded at the Hong Kong Observatory was 34.9 degrees Celsius at 1321 HKT on 3 August. The minimum air temperature recorded at the Hong Kong Observatory was 9.4 degrees Celsius at 0801 HKT on 10 January and at 0523 HKT on 28 December. The maximum gust peak speed recorded at Waglan Island was 139 kilometres per hour from 080 degrees at 2133 HKT on 14 September. The maximum instantaneous rate of rainfall recorded at King's Park exceeded [320] millimetres per hour at 0828 HKT on 24 March. # Reduced visibility refers to visibility below 8 kilometres when there is no fog, mist, or precipitation. - The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend. - Before 10 October 2007, the number of hours of reduced visibility at the Hong Kong International Airport in 2005 and thereafter displayed in this web page was based on hourly visibility observations by professional meteorological observers. Since 10 October 2007, the data have been revised using the average visibility readings over the 10-minute period before the clock hour, as recorded by the visibility meter near the middle of the south runway. * 1971-2000 Climatological Normal, unless otherwise specified § 1997-2008 Mean value [ ] upper limit of recorder ( ) Total for 30 days ^ In case the data are not available from Waglan Island, observations of Cheung Chau or other nearby weather stations will be incorporated in computing the Prevailing Wind Direction and Mean Wind Speed |