MCA CoC Meteorology at Sea — Questions and Answers
Question 1: In the Northern Hemisphere, according to Buys Ballot's Law, if you stand with your back to the wind, where is the centre of a low-pressure system located?
- Directly behind you
- To your right and slightly ahead
- To your left and slightly ahead (Correct answer)
- Directly in front of you
Correct answer: To your left and slightly ahead
Buys Ballot's Law states that in the Northern Hemisphere, if you stand with your back to the wind, the low-pressure centre is to your left and slightly ahead. This is because wind flows anticlockwise around a low in the Northern Hemisphere (due to the Coriolis effect), and surface friction causes the wind to cross the isobars at an angle towards the low centre.
Question 2: What are the typical warning signs that a tropical cyclone is approaching a vessel in the North Atlantic?
- A steady barometer, clear skies, and calm seas
- A falling barometer (diurnal variation disrupted), long ocean swell from an unusual direction, high cirrus clouds, and increasing wind (Correct answer)
- Rising barometer and fog formation
- Sudden temperature increase and calm winds
Correct answer: A falling barometer (diurnal variation disrupted), long ocean swell from an unusual direction, high cirrus clouds, and increasing wind
Approaching tropical cyclones in the North Atlantic are typically preceded by: disruption of the normal diurnal barometric variation (the barometer fails to rise at 1000 and 2200), long ocean swell arriving from the direction of the storm, high cirrus clouds (mare's tails) followed by lower cloud, a backing and freshening wind, and often a coppery or threatening sky appearance.
Question 3: What is the 'dangerous semicircle' of a tropical cyclone in the Northern Hemisphere, and why is it dangerous?
- The left half facing the direction of movement — wind drives vessels away from the storm
- The right half facing the direction of movement — the cyclone's forward motion adds to the wind speed and tends to drive vessels into the storm's path (Correct answer)
- The eye of the storm — where winds are calm but seas are chaotic
- The rear quadrant — where rainfall is heaviest
Correct answer: The right half facing the direction of movement — the cyclone's forward motion adds to the wind speed and tends to drive vessels into the storm's path
In the Northern Hemisphere, the dangerous semicircle is the right half of the storm when facing the direction of travel. Here, the rotational wind speed adds to the storm's forward speed, producing the strongest winds. Additionally, the wind pattern tends to drive vessels towards the storm's projected path, making escape more difficult. The left semicircle is the 'navigable semicircle' where winds tend to push vessels away from the track.
Question 4: What does the term 'veering' mean in meteorological terminology as used in UK weather forecasts?
- Wind decreasing in strength
- Wind direction changing clockwise (e.g., from south to west) (Correct answer)
- Wind direction changing anticlockwise
- Wind increasing in gusts
Correct answer: Wind direction changing clockwise (e.g., from south to west)
In meteorology, 'veering' means the wind direction changes clockwise (e.g., from south through west to north). The opposite, 'backing', means an anticlockwise change. In the Northern Hemisphere, a veering wind is often associated with the passage of a warm front or the approach of a high-pressure system, while backing winds may indicate the approach of a low.
Question 5: On the Beaufort Scale, what wind speed range and sea conditions are associated with Force 8 (Gale)?
- 17-21 knots, moderate waves with whitecaps
- 28-33 knots, high waves with dense foam streaks
- 34-40 knots, moderately high waves with breaking crests and spindrift (Correct answer)
- 48-55 knots, very high waves with heavy sea spray
Correct answer: 34-40 knots, moderately high waves with breaking crests and spindrift
Beaufort Force 8 (Gale) corresponds to wind speeds of 34-40 knots (39-46 mph). Sea conditions include moderately high waves of greater length, edges of crests begin to break into spindrift, foam is blown in well-marked streaks along the direction of the wind. This is the threshold at which the MCA issues gale warnings for UK waters.
Question 6: What meteorological information is provided in the UK Shipping Forecast broadcast by the BBC, and how often is it issued?
- Wind direction and force for major ports only, issued weekly
- Gale warnings, general synopsis, and area forecasts for 31 sea areas around the British Isles, issued four times daily (Correct answer)
- Rainfall forecasts for coastal regions, issued twice daily
- Satellite imagery descriptions for the North Atlantic, issued daily
Correct answer: Gale warnings, general synopsis, and area forecasts for 31 sea areas around the British Isles, issued four times daily
The UK Shipping Forecast is issued by the Met Office and broadcast by BBC Radio 4 at 0048, 0520, 1201, and 1754 UTC. It covers 31 sea areas and includes: any gale warnings in force, a general synopsis describing pressure systems and fronts, and area forecasts giving wind direction and force, sea state, weather, and visibility for each area.
MCA CoC Meteorology at Sea
In the Northern Hemisphere, according to Buys Ballot's Law, if you stand with your back to the wind, where is the centre of a low-pressure system located?