Climate
The climate of Hong Kong is a monsoon-influenced humid subtropical climate (Köppen climate classification Cwa), just short of being a tropical wet-and-dry climate. As with other subtropical areas, Hong Kong has long summers and winters, and comparatively short springs and autumns.
Climate
In the winter, temperatures hover between 15 °C and 20 °C. However, northeast winter monsoons bring frequent cold fronts which can cause the temperature to dip below 10 °C, despite Hong Kong's tropical latitude and coastal location. Conversely, warm maritime airstreams commonly raise the temperature well above 20 °C; temperatures as high as 29 °C have been recorded in February. Winter usually starts sunny in December and becomes cloudier towards February.
Spring brings warmer and more humid weather. There is a sharp increase in rainfall around April. Spring is the cloudiest season of the year, with March and April both averaging only around 100 hours of bright sunshine.
Summer weather is hot, humid and unstable. Although it is usually sunny, thunderstorms and scattered showers are common. August has the highest average rainfall in the year. Temperatures usually exceed 30 °C during the day, which, coupled with a high humidity, can result in an extreme heat index. Extreme heat indices are also caused by continuous sunshine and low breeze, usually long-lasting around July and August, as a result of subtropical high pressure areas. This also occurs before a typhoon hits Hong Kong or nearby regions in the northeast, e.g. Taiwan or the Eastern Coast of China, which frequently happens in the summer. Such an outbound airstream brings even hotter weather, in addition to dirtier air. Nights are warm with an average minimum temperature of 26 °C.
Autumn is generally considered the most pleasant season. Temperatures are still high (20–27 °C) but humidity and rainfall are considerably lower. Autumn is also the sunniest season in Hong Kong, with October and November both averaging close to 200 hours of bright sunshine.
| Climate data for Hong Kong (1981–2010) | ||||
|---|---|---|---|---|
| Month | June | July | August | September |
| Avg high °C (°F) | 30.2 (86.4) | 31.4 (88.5) | 31.1 (88.0) | 30.1 (86.2) |
| Daily Mean °C (°F) | 27.9 (82.2) | 28.8 (83.8) | 28.6 (83.5) | 27.7 (81.9) |
| Avg Low °C (°F) | 26.2 (79.2) | 26.8 (80.2) | 26.6 (79.9) | 25.8 (78.4) |
| Rainfall mm (in) | 456.1 (17.951) | 376.5 (14.823) | 432.2 (17.016) | 327.6 (12.898) |
| % Humidity | 82 | 81 | 81 | 78 |
| Avg Rainy Days (≥ 0.1 mm) | 19.07 | 17.60 | 16.93 | 14.67 |
| Sunshine hours | 146.1 | 212.0 | 188.9 | 172.3 |
Severe weather warnings
During August, Hong Kong can come under the threat of a typhoon and rainstorm. In case of such severe weather conditions, the Hong Kong Observatory will issue suitable warnings, which will affect part of the daily life in Hong Kong, as some public and commercial facilities will shut down. However, most of the MTR will maintain limited services even in the worst weather conditions.
Rainstorm warning signals
The rainstorm warning signals (暴雨警告訊號) are a set of signals used in Hong Kong to alert the public about the occurrence of heavy rain which is likely to bring about major disruptions such as traffic congestion and floods. They also ensure a state of readiness within the essential services to deal with emergencies.
AMBER rainstorm signal
Heavy rain has fallen or is expected to fall generally over Hong Kong, exceeding 30 millimeters in an hour, and is likely to continue.
The AMBER signal gives alert about potential heavy rain that may develop into RED or BLACK signal situations. There will be flooding in some low-lying areas and poorly drained areas.
RED rainstorm signal
Heavy rain has fallen or is expected to fall generally over Hong Kong, exceeding 50 millimeters in an hour, and is likely to continue.
The RED signal gives alert about potential heavy rain that may develop into BLACK signal situations. All students are to remain at school unless there is a visible risk to staying in the building.
BLACK rainstorm signal
Very heavy rain has fallen or is expected to fall generally over Hong Kong, exceeding 70 millimeters in an hour, and is likely to continue.
When the BLACK signal is issued, Hong Kong will come to a complete standstill. Schools will not dismiss students unless there is a visible risk to staying at school, and everyone is recommended to seek shelter immediately. Buses and other forms of public transport may be halted after a while to allow commuters to go home, depending on demand and the level of risk along the route. MTR services will be limited or suspended because of the risk of flooding.
The RED and BLACK signals warn the public of heavy rain which is likely to bring about serious road flooding and traffic congestion. They will trigger response actions by Government departments and major transport and utility operators. The public will be given clear advice on the appropriate actions to take.
Tropical cyclone warning signals
The tropical cyclone warning signals (熱帶氣旋警告信號) or informally typhoon signals (颱風信號) are a set of signals used to indicate the threat or effects of a tropical cyclone. The Hong Kong Observatory issues the warning signal if a tropical cyclone is centred within 800 km (500 miles) of Hong Kong and may affect Hong Kong later.
| Signal- Number | Signal- Name | Sustained Wind Speed- (km/h, (mph, Beaufort scale)) | Gusts- (km/h (mph)) | Signal- Sign | Remarks |
|
1 |
Stand-by (戒備) |
N/A |
N/A |
 |
A tropical cyclone is centred within 800 kilometres of Hong Kong and may later affect the territory, or there are strong winds in Hong Kong waters |
|
3 |
Strong winds (強風) |
41–62 (26–37, Beaufort Force 6–7) |
may exceed 110 (69) |
 |
Strong winds are expected or blowing generally in Hong Kong near the sea level, and the wind condition is expected to persist |
|
8 NE / 8 NW / 8 SE / 8 SW |
Gale or storm force winds-(烈風或暴風) |
63–117 (38–73, Beaufort Force 8–11) |
may exceed 180 (113) |
 |
Gale or storm force winds are expected or blowing generally in Hong Kong near the sea level from the NE/ NW/ SE/ SW quadrant, and the wind condition is expected to persist |
|
9 |
Increasing- gale or storm force winds-(烈風或暴風風力增強) |
88–117, increasing (55–73, Beaufort Force 10–11) |
N/A |
 |
Gale or storm force winds are increasing. |
|
10 |
Typhoon(颶風) |
>118 (74+, Beaufort Force 12) |
may exceed 220 (138) |
| Hurricane force winds. Eye of typhoon may be passing directly over Hong Kong. |