Beaufort scale the extension to 17 noted above. China also switched to this extended version without prior notice on the morning of 15 May 2006, and the extended scale was immediately put to use for Typhoon Chanchu. Hong Kong and Macau retain force 12 as the maximum. In the United States, winds of force 6 or 7 result in the issuance of a small craft advisory, with force 8 or 9 winds bringing about a gale warning, force 10 or 11 a storm warning ("a tropical storm warning" being issued instead of the latter two if the winds relate to a tropical
Wind stress of heat and mass between the water and the atmosphere. The air blowing parallel to a water body imparts motion to the surface water by shear action. This is a downward transfer of momentum from the air to the water that ultimately generates a drift current underneath. The water surface also deforms under the action of wind and becomes wavy for increasing wind speeds, which modifies the grip that the wind has on the surface itself. The mechanics of the interaction between wind and water becomes thus increasingly complex. The Beaufort scale, for example, shows the correspondence between wind speed