Here is a little explanation of the unit equivalences used on Winds-Up.

The knot is the main unit of measurement of the wind in the maritime sector.
It stands for a move of a nautic mile in an hour, i.e 1.852 km/h or 0.514 m/s.
All our weather stations record wind news in knots.

The kilometre per hour is the more frequent unit of measurement for speed in our daily life (navigation excluded).
It comes from an unit basis which is the meter per second (m/s).
As for the Anglo-saxon system, it uses the mile per hour (pmh).

The mile per hour, mph symbol, is a unit of measurement used for speed in nautical meteorology.
It is also used as unit of measurement used for speed on roads in some countries of United Kingdom.

The land mille measures approximately 1609 meters, whereas the nautic mille is equivalent to 1852 meters.

The meter per second is the unit of speed used in the international system.
It defines in meters the traveled distance per second.

The Beaufort scale is an empirical measure that relates wind strength to observed conditions at sea or on land on a scale going from 0 to 12.
The scale was devised in 1805 by Francis Beaufort. Initially destinated to improve the concision and precision of logbooks, it is now universally used in nautical meteorology.

The creation of the Beaufort scale has been developed and adapted over years. The last adaptation dates from 1946.