Meteorology
Meteorology questions in Part A are about Hong Kong's weather systems and what they mean for a small vessel: monsoon strength, typhoon signals, squalls and visibility. You are expected to read a synoptic situation, not to forecast professionally.
Pressure and wind
- Close isobars mean strong wind; the wind crosses isobars at an angle toward low pressure.
- Buys Ballot in the Northern Hemisphere: stand with your back to the wind and low pressure lies on your left.
- A falling barometer with a backing or veering wind warns of an approaching low or front.
Hong Kong seasons
- Northeast monsoon, roughly November to March: cool, dry, strong easterlies, good visibility but rough seas in the eastern approaches.
- Southwest monsoon, roughly May to September: hot, humid, unstable air, heavy showers and violent squalls.
- Spring brings sea fog and reduced visibility; summer brings thunderstorms and waterspouts.
Typhoons and warnings
- The Hong Kong Observatory issues signals 1, 3, 8 (northeast, southeast, southwest, northwest), 9 and 10. Signal 8 means gale or storm force winds expected, with the direction indicating where the wind will come from.
- Only a small area experiences the eye; the dangerous semicircle in the Northern Hemisphere is the right-hand side of the track.
- Rainstorm warnings, amber, red and black, indicate the rainfall rate and warn of flooding and poor visibility.
Worked example
You are southwest of Hong Kong. The wind is northeast force 6 and the pressure is falling.
Reasoning: the wind blows from 045°, toward 225°. Facing 225°, low pressure is on your left, bearing 135° - southeast of you. Steering northwest opens the range from the centre. A falling barometer confirms the system is approaching, not departing.
Traps
- Confusing wind 'from' and wind 'toward'.
- Assuming Signal 8 means a direct hit; it means gale or storm force winds.
- Ignoring a squall line in summer.
- Treating a rising barometer after a front as settled weather without checking the next system.