The Thunderstorm after midnight of the Mid Autumn Festival

In response to reports and commentaries by the mass media on the thunderstorm after midnight of the Mid Autumn Festival, the Hong Kong Observatory would like to make the following points:

1. The thunderstorm, which occurred during the early morning of 22 September 2002, was an isolated weather system. Its formation and dissipation were erratic in nature. To predict it accurately is beyond the current state of the science.
2. The rainfall distribution map of Guandong and its vicinity shows that the heavy rain this time is confined to the territory of Hong Kong. Over 80 mm of rainfall were recorded at the Hong Kong Observatory Headquarters while no rain or very little rain was reported in other major cities nearby.
3. The extent of thunderstorms is typically small and uneven. When it is raining heavily in one place, there may not be any rain in other areas. Moreover, the intensity and movement of thunderstorms change rapidly rendering its forecast rather difficult with rather short forecast range. Generally speaking for Hong Kong, which is on the coast in the sub-tropics, modern technology cannot predict the exact location, timing and the amount of rainfall associated with thunderstorms for more than an hour in advance.
4. Before and during major holidays, as large-scale public events are often involved, the Observatory routinely strengthens its forecast operations. Due to the limitation of technology, the isolated and sudden change in weather this time was not forecast in time. The understanding of the public in this regard would be much appreciated.
5. The Observatory will continue its ongoing efforts in research and development to use radar, satellite and numerical weather prediction techniques in the forecast of isolated heavy rain. Moreover, the Observatory will make an effect to learn from this event with a view to improving its forecast in future.