Depression

A low-pressure weather system that can cause adverse sea conditions, including strong winds and rough seas.

A depression is a meteorological phenomenon characterised by an area of low atmospheric pressure, often associated with unsettled weather conditions. In the marine environment, depressions are significant because they can lead to the development of strong winds, increased wave heights, and potentially dangerous sea conditions. These systems typically form when warm air rises and cooler air moves in to replace it, creating a cyclonic circulation. The strength of the winds and the severity of the sea state depend on the pressure gradient—the difference in pressure between the centre of the depression and the surrounding areas. The tighter the gradient, the stronger the winds. 

Depressions are often associated with fronts, which are boundaries between different air masses. As a depression moves, it can bring a sequence of weather changes, including rain, squalls, and sometimes thunderstorms. Mariners must pay close attention to weather forecasts and barometric pressure readings to anticipate the approach of a depression. Navigating through or near a depression can be hazardous, so prudent skippers will often alter course or delay voyages to avoid these systems. Understanding the behaviour of depressions is crucial for safe passage planning and ensuring the safety of both crew and vessel.