Air MassAn extensive body of the atmosphere whose physical properties, particularly temperature and humidity, exhibit only small and continuous differences in the horizontal. It may extend over an area of several million square kilometres and over a depth of several kilometres.
Backing WindCounter-clockwise change of wind direction, in either hemisphere.
Beaufort ScaleWind force scale, original based on the state of the sea, expressed in numbers from 0 to 12.
FetchDistance along a large water surface trajectory over which a wind of almost uniform direction and speed blows.
FogSuspension of very small, usually microscopic water droplets in the air, generally reducing the horizontal visibility at the Earth's surface to less than 1 km.
FrontThe interface or transition zone between air masses of different densities (temperature and humidity).
Gale Force WindWind with a speed between 34 and 47 knots. Beaufort scale wind force 8 or 9.
GustSudden, brief increase of the wind speed over its mean value.
HazeSuspension in the atmosphere of extremely small, dry particles which are invisible to the naked eye but numerous enough to give the sky an opalescent appearance.
HighRegion of the atmosphere where the pressures are high relative to those in the surrounding region at the same level.
HurricaneName given to a warm core tropical cyclone with maximum surface winds of 118 km/h (64 knots) or greater in the North Atlantic, the Caribbean, the Gulf of Mexico and in the Eastern North Pacific Ocean.
KnotUnit of speed equal to one nautical mile per hour. (1.852 km/h)
Land BreezeWind of coastal regions, blowing at night from the land towards a large water surface as a result of the nocturnal cooling of the land surface.
Line SquallSquall which occurs in a line.
LowRegion of the atmosphere in which the pressures are lower then those of the surrounding regions at the same level.
MistSuspension in the air of microscopic water droplets which reduce the visibility at the Earth's surface.
PressureForce per unit area exerted by the atmosphere on any surface by virtue of its weight; it is equivalent to the weight of a vertical column of air extending above a surface of unit area to the outer limit of the atmosphere.
RidgeRegion of the atmosphere in which the pressure is high relative to the surrounding region at the same level.
Sea BreezeWind in coastal regions, blowing by day from a large water surface towards the land as a result of diurnal heating of the land surface.
Sea FogFog which forms in the lower part of a moist air mass moving over a colder surface (water).
Sea StateLocal state of agitation of the sea due to the combined effects of wind and swell.
SquallAtmospheric phenomenon characterizes by an abrupt and large increase of wind speed with a duration of the order of minutes which diminishes suddenly. It is often accompanied by showers or thundershowers.
Storm Force WindWind with a wind speed between 48 and 63 knots. Beaufort scale wind force 10 or 11.
Storm SurgeThe difference between the actual water level under influence of a meteorological disturbance (storm tide) and the level which would have been attained in the absence of the meteorological disturbance (i.e. astronomical tide).
SwellAny system of water waves which has left its generating area.
ThunderstormSudden electrical discharge manifested by a flash of light and a sharp or rumbling sound. Thunderstorms are associated with convective clouds and are, more often, accompanied by precipitation in the form of rain showers, hail, occasionally snow, snow pellets, or ice pellets.
Tropical CycloneGeneric term for a non-frontal synoptic scale cyclone originating over tropical or sub-tropical waters with organized convection and definite cyclonic surface wind circulation.
Tropical DepressionWind speed up to 33 knots.
Tropical DisturbanceLight surface winds with indications of cyclonic circulation.
Tropical StormMaximum wind speed of 34 to 47 knots.
TroughAn elongated area of relatively low atmospheric pressure.
VeeringClockwise change of wind direction, in either hemisphere.
VisibilityGreatest distance at which a black object of suitable dimensions can be seen and recognized against the horizon sky during daylight or could be seen and recognized during the night if the general illumination were raised to the normal daylight level.
WaterspoutA phenomenon consisting of an often violent whirlwind revealed by the presence of a cloud column or inverted cloud cone (funnel cloud), protruding from the base of a cumulonimbus, and of a bush composed of water droplets raised from the surface of the sea. Its behaviour is characterized by a tendency to dissipate upon reaching shore.
Wave HeightVertical distance between the trough and crest of a wave.
Wave PeriodsTime between the passage of two successive wave crests past a fixed point.