Meteorology and Oceanography
This domain tests weather interpretation and ship handling in weather: pressure systems and isobars, Buys Ballot, tropical revolving storms and avoidance, fronts and fog, sea state, currents and swell, and weather routeing.
Pressure and wind
Isobars show the pressure gradient: the closer they are, the stronger the wind. In the Northern Hemisphere wind blows anticlockwise around a low and clockwise around a high, crossed toward low pressure by roughly 10 to 20 degrees over the sea because of surface friction. Buys Ballot: in the Northern Hemisphere, with your back to the wind, low pressure bears on your left, slightly forward; in the Southern Hemisphere it is on your right.
Tropical revolving storms
Structure: eye, eyewall of strongest winds, spiral bands. They form over warm water (about 27°C or more), move westward in the trade-wind belt and recurve poleward. In the Northern Hemisphere the left-hand semicircle (looking along the track) is the dangerous semicircle, where the wind sets a ship toward the track; the right-hand is the navigable semicircle. Wind veering indicates the right-hand semicircle, wind backing the left-hand. Avoid the storm by the shortest route: never try to cross ahead of a TRS.
Fog, fronts and sea state
Warm fronts give advection fog ahead of them; a cold front brings squalls and a sharp wind veer. Use the Beaufort scale for wind and sea state, remember swell can outrun its generating wind, and note the diurnal sea breeze and land breeze.
Worked example
In the Northern Hemisphere the wind is NE and the barometer has fallen 4 hPa in three hours. With your back to the wind you face 225°T; the centre bears about 90° to the left, roughly 135°T, i.e. to the SE. If the storm is moving WNW, then the reciprocal bearing from the centre is about NW, putting the ship just right of the track, the navigable semicircle. Wind will veer, confirming this. Action: keep the wind on the starboard quarter and make best speed away from the track.
Traps
- Applying Buys Ballot to the wrong hemisphere.
- Judging the semicircle from the wind direction alone without the storm's track.
- Confusing backing and veering.