Handbook 
Weather now:
ARRANGEMENTS DURING BAD WEATHER
When Tropical Storm Warning Signal No. 8 (or a higher number) or the Black Rainstorm Warning Signal is hoisted, the following arrangements will apply:
(a) For classes and examinations not yet started| If either of the warnings is hoisted or in force at or after 6:00 a.m. | All morning classes and examinations commencing before 2:00 p.m. will be cancelled automatically. |
| If either of the warnings is hoisted or in force at or after 11:00 a.m. | All afternoon classes and examinations commencing at any time from 2:00 p.m. and before 6:00 p.m. will be cancelled automatically. |
| If either of the warnings is hoisted or in force at or after 3:00 p.m. | All evening classes and examinations commencing from 6:00 p.m. onward will be cancelled automatically. |
(b) For classes and examinations already started
| When Tropical Storm Warning Signal No. 8 or above is hoisted | - All classes will be suspended immediately. - All examinations will continue until the end of that examination session. |
| When Black Rainstorm Warning Signal is hoisted | - All classes and examinations, except those held outdoors, will continue. - For outdoor classes and examinations, the responsible staff members on the spot should suspend the activities immediately, ensure that all students are taken to a safe place, and remain there until it is safe for them to return home. |
When Tropical Storm Warning Signal No. 3 or Red Rainstorm Warning Signal is in force, it should be assumed that all classes and examinations will be held as scheduled unless an announcement to the contrary has been made by the University.
source: http://www.asa.hku.hk/weather.htm