Squall

A squall is a sudden, rapid increase in wind speed, typically accompanied by a shift in wind direction, a drop in barometric pressure, heavy rain or hail, and reduced visibility. Squalls may occur as isolated events or as part of a line — a squall line — associated with a cold front or convective instability. In the tropics, squalls are frequent and intense, arising from convective cells without the frontal mechanisms common in temperate latitudes. ICAO Annex 3 defines reporting criteria for squalls in aviation and marine meteorological observations. For a watchkeeping officer, a squall requires immediate action. The sudden increase in wind — which can jump from 10 knots to 40 knots or more in a matter of minutes — can cause a vessel to heel unexpectedly, particularly if sails are set or deck cargo or hatch covers offer significant wind resistance. Orders to reduce speed, check deck equipment, and alert the master should be issued without delay when a squall appears on radar as a bright return or is observed visually as a dark, fast-moving cloud line. Squalls are particularly hazardous during cargo operations at anchorage, where a sudden increase in wind can part a mooring line or swing the vessel into shallow water. Weather observations that include squall activity must be reported to national meteorological services as part of the Voluntary Observing Ship programme, since squall data improves storm tracking. Deck logs should record squall occurrences with the time, position, wind speed before and after, barometric change, and any actions taken.