The above diagram shows the past 72-hour backward trajectory of air mass reaching Hong Kong at a height of 100 metres above ground level ending at 8 a.m.
The product may be useful for tracing the origin of air mass reaching Hong Kong. Please click here for cases of the backward trajectory map under different weather patterns.
Normally, this web page will be updated daily at around 5 p.m.
Archive of trajectories is available for the past 30 days.
The trajectory was prepared using the HYSPLIT model of NOAA. Anyone wishing to quote or further disseminate the data should read the "Disclaimer" of the NOAA Air Resources Laboratory web site for details.
Incomplete analysis will be supplemented by forecast data.