On passage from the UK to the Grand Banks in June, you encounter fog. Your examiner asks you to identify the type of fog and explain why it forms here.

A. ADVECTION FOG — the dominant fog type on the Grand Banks. Mechanism: warm, moist air from the Gulf Stream (sea surface temperature 15-20°C) flows northward and encounters the cold Labrador Current (SST 2-8°C). The warm air is cooled below its dew point by contact with the cold sea surface, causing condensation — fog forms. Characteristics: persists regardless of time of day (unlike radiation fog which disperses with daytime heating); very dense, may last days; geographically fixed to the temperature boundary zone. Other fog types: Radiation Fog — over land, forms on calm clear nights as the land surface cools; disperses with morning sun; does not persist at sea. Sea Smoke (Arctic Sea Smoke) — cold dry air over relatively warm water; water vapour condenses immediately above the surface into low wisps — opposite mechanism to advection fog. Avoidance: route planning to avoid the Grand Banks fog zone (approximately 43°-47°N, 45°-55°W) in spring/summer; alternative routes further north or south.

B. Radiation fog forms on the Grand Banks because the sun cannot penetrate the ocean and heats the sea surface at night. This is the most common fog type at sea.

C. Grand Banks fog is frontal fog forming ahead of Atlantic depressions. It is associated with the warm front and disperses when the front passes.

D. Steam fog forms when the cold Labrador Current water evaporates into the warm overlying air. This is only 1-2 metres deep and does not significantly affect navigation.

A. Buys Ballot's Law (Northern Hemisphere): stand with your back to the wind — the centre of lowest pressure (the depression) lies approximately 90° to 120° to your LEFT (and slightly forward). Wind from SW, standing with back to SW means facing NE — the depression centre lies to the NW or NNW of your position. Backing wind (SW to S) means the depression is approaching from the west or northwest — you are in the WARM SECTOR of an approaching depression (between the warm front and cold front). Expected sequence: (1) Barometer continues to fall; (2) Wind continues to back and freshen; (3) Warm front will pass with steady rain; (4) Wind veers to W-NW as cold front arrives; (5) Violent squalls, heavy rain, and rapid pressure rise as the cold front passes; (6) Barometer rises rapidly; (7) Wind veers to NW-N; clearing showers with good visibility.

B. Stand facing the wind — the depression lies 90° to your right. Wind from the SW means the depression is to the NW. Veering wind means the depression is passing to the south.

C. Buys Ballot's Law only applies in the Southern Hemisphere. In the Northern Hemisphere, the depression lies to the right of the wind direction.

D. A falling barometer at 2 hPa/hour indicates a stationary anticyclone nearby. The backing wind confirms high pressure to the east.

A. Tropical Revolving Storm (TRS) warning signs: barometer below 1000 hPa and falling; confused swell from a direction other than the wind (the swell propagates ahead of the storm from the storm centre); backing wind in the Northern Hemisphere (NE backing to N indicates approach from the NW); sky colour — "dirty" yellow-orange sunset; rapid cloud development. In the North Indian Ocean in June: this is the SW monsoon season — TRS season (April-June and October-December in the Indian Ocean). Avoidance manoeuvre — NAVIGABLE SEMICIRCLE RULE (Northern Hemisphere): The right/starboard side of the storm track is the DANGEROUS SEMICIRCLE (winds combine with the track velocity, vessel may be drawn into the storm path). The left/port side is the NAVIGABLE SEMICIRCLE (safer, though still dangerous). Action from Northern Hemisphere vessel facing INTO the wind: storm bears 10 points (112°) to the RIGHT — put the wind on the starboard quarter (135°) and make best speed. This keeps you in the navigable semicircle and opens distance from the storm.

B. Heave to and take the storm on the bow. A vessel hove-to rides a tropical cyclone most safely and minimises ground track movement.

C. Alter course to run directly away from the storm at maximum speed. The fastest route away is always directly astern of the storm's current position.

D. A backing wind in the Northern Indian Ocean means the TRS is to your east. Steam into the storm on the navigable (right) side to cross its track before it intensifies.