Maximum sustained wind 50% of the geostrophic wind speed aloft; while over open water or ice, the reduction is between 10% and 30%. In most basins, maximum sustained winds are used to define their category. In the Atlantic and northeast Pacific oceans, the Saffir–Simpson scale is used. This scale can be used to determine possible storm surge and damage impact on land. In most basins, the category of the tropical cyclone (for example, tropical depression, tropical storm, hurricane/typhoon, super typhoon, depression, deep depression, intense tropical cyclone) is determined from the cyclone's maximum sustained wind. Only in Australia is this quantity not used to
Beaufort scale during the voyage of HMS "Beagle" under Captain Robert FitzRoy, later to set up the first Meteorological Office (Met Office) in Britain giving regular weather forecasts. In the early 19th century, naval officers made regular weather observations, but there was no standard scale and so they could be very subjective – one man's "stiff breeze" might be another's "soft breeze". Beaufort succeeded in standardising the scale. The initial scale of thirteen classes (zero to twelve) did not reference wind speed numbers but related qualitative wind conditions to effects on the sails of a frigate, then the main ship of the