Meteorology at Sea Flashcards

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?

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.

What are the typical warning signs that a tropical cyclone is approaching a vessel in the North Atlantic?

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.

What is the 'dangerous semicircle' of a tropical cyclone in the Northern Hemisphere, and why is it dangerous?

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.

What does the term 'veering' mean in meteorological terminology as used in UK weather forecasts?

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.

On the Beaufort Scale, what wind speed range and sea conditions are associated with Force 8 (Gale)?

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.

What meteorological information is provided in the UK Shipping Forecast broadcast by the BBC, and how often is it issued?

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.