9-day Weather Forecast for Hong Kong

Forecast: maximum temperature minimum temperature 50% of the days have maximum temperatures falling within this range (based on 30-year climate data) 50% of the days have maximum temperatures falling within this range (based on 30-year climate data)[note 1] 50% of the days have minimum temperatures falling within this range 50% of the days have minimum temperatures falling within this range (based on 30-year climate data)[note 1] Extended Outlook

Forecast: maximum relative humidity minimum relative humidity 50% of the days have maximum relative humidity falling within this range (based on 30-year climate data) 50% of the days have maximum relative humidity falling within this range (based on 30-year climate data)[note 1] 50% of the days have minimum relative humidity falling within this range (based on 30-year climate data) 50% of the days have minimum relative humidity falling within this range (based on 30-year climate data)[note 1]

Automatic Regional Weather Forecast in Hong Kong & Pearl River Delta Region
Climatological information for {2}-{3}

1. This middle 50% range (between 25th and 75th percentiles) is calculated based on the maximum/minimum temperature and relative humidity data within a 5-day period centred on that day in the 30 years from 1991 to 2020.
2. "9-day Weather Forecast" provides general indications of the trends in weather for the coming 9 days. For detailed description of today's weather forecast, please refer to "Local Weather Forecast".
3. The Probability of Significant Rain (PSR) forecast provides users with additional reference on rainfall amount and forecast trend for the coming 9 days. The PSR forecast on each day indicates the probability of the accumulated rainfall generally over Hong Kong reaching 10 mm (i.e. around the mean daily rainfall in rainy season) or more on that day. There are 5 categories of probability as follows:

High>=70%		For every 100 forecasts with a "high" probability, there are about 70 times or more with an average accumulated rainfall of 10 mm or above in actual observation.
Medium High 55-69%		For every 100 forecasts with a "medium high" probability, there are about 55 to 69 times with an average accumulated rainfall of 10 mm or above in actual observation.
Medium 45-54%		For every 100 forecasts with a "medium" probability, there are about 45 to 54 times with an average accumulated rainfall of 10 mm or above in actual observation.
Medium Low 30-44%		For every 100 forecasts with a "medium low" probability, there are about 30 to 44 times with an average accumulated rainfall of 10 mm or above in actual observation.
Low<30%		For every 100 forecasts with a "low" probability, there are about less than 30 times with an average accumulated rainfall of 10 mm or above in actual observation.

1. The accuracy of forecast generally decreases while the error generally increases with forecast period. For forecast elements in "9-day Weather Forecast" other than PSR, the average accuracy for the next one to three days, four to seven days, and eight to nine days are about 90%, 85% and 80% respectively. The errors of PSR forecast in the next one to six days are within around 10% and those in seven to nine days are within around 20%.
2. The accuracy and error of forecast also vary for different weather systems in different seasons. Generally speaking, weather in spring and summer such as fog, tropical cyclone and severe convective weather is more changeable, resulting in higher uncertainty of forecast.