By using computer model analyses, the past 72-hour backward trajectory of the air mass reaching Hong Kong is estimated by the Observatory on a daily basis. The daily trajectories are compiled into the Monthly Backward Trajectory Map. The Monthly Map for October 2010 is now available on the following webpage:
As revealed from the figure below, the air masses reaching Hong Kong in October 2010 mainly originated from north and northeast of Hong Kong. It is because Hong Kong was affected by the northeast monsoon most of the time in the month.
Backward Trajectory of Air Mass reaching Hong Kong in October 2010