This webpage shows the 72-hour trajectory of the forecast movement of the air reaching Hong Kong at a height of 100 metres above ground level ending at 8 a.m. or 8 p.m. of the next 2 to 3 days.

The product may be useful for tracing the origin of air reaching Hong Kong.

Points to note:

• Normally, this web page will be updated daily at around 2 a.m. and 2 p.m.
• 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.

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