1. The products provide hourly forecasts of air temperature, relative humidity and wind direction and speed for the next seven days at 15 stations over Hong Kong. Users can visualize the products in time series or animation. The products are updated twice a day roughly before midnight and noon each day.
2. The products are generated using a multi-model consensus forecast system, which integrates the outputs of a number of global numerical weather prediction (NWP) models as well as the mesoscale model of the Hong Kong Observatory. The model outputs are first corrected based on the observed data collected at different stations. A consensus forecast is then derived by combining the corrected model forecasts weighted according to their past performance. Technical details of the forecast system are available from this paper.
3. The icon on the map shows the forecast for wind direction and speed. icon The number inside the circle indicates the forecast wind speed in kilometres per hour. The red arrow head points in the direction, to which the forecast wind will blowing. In the above example, the wind is forecast to be 23 kilometres per hour from the southeast (i.e. from the southeast towards the northwest).
4. In the time series chart for wind speed, the black arrow represents the hourly forecast wind direction. "←" and "↓" indicate easterly and northerly winds respectively. Wind Speed Time Series
5. Since the production of forecasts requires observations from weather stations, no forecast could be generated for a station if the observed data are not available due to station maintenance or other reasons. In this case, an "M" will be displayed.
6. Apart from the above-mentioned weather elements, daily forecasts on the probability of precipitation (PoP) over Hong Kong are also provided. PoP indicates the chance of rain (having rainfall of 0.5 mm or more) in Hong Kong on a certain day and it has six categories: <20%, 20%, 40%, 60%, 80% and >80%.
7. For example, if PoP is 60%, it means that the probability of rain occurrence over the territory is around 60% on that day. In other words, rain occurs about 60 times on average in every 100 forecasts, with the error of around 10 times on average from the actual number of occurrence according to the verification statistics. It should be noted that PoP only indicates how likely there will be rain, it is not directly related to the size of area affected by rain, the time of rain occurrence, its duration or intensity.
8. As the products integrate the outputs of a number of NWP models, error in individual NWP model forecasts will limit the capability of the products in predicting extreme weather events.
9. The above products are directly output from a computer forecast system without manual adjustment. The forecast weather conditions may be different from the weather forecast issued by the Observatory or those recorded at individual weather station. Please refer to the official forecasts issued by the Observatory.
10. For more information on numerical weather prediction, probabilistic forecast and other meteorological knowledge, please visit: Simulating Atmosphere Butterfly Effect, Model Ensemble and Probabilistic Forecast Educational Resources Glossary of Some Meteorological Terms
11. The background geographical information on this page comes from Google Maps and the usage is subject to Google's Terms of Use. The downloading speed depends on the responsiveness of its servers and sometimes it may take a longer time to complete the download.
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