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Tropical cyclone warnings and watches
Tropical cyclone warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate preparation for the cyclone, including evacuation of vulnerable areas where necessary. It is important that interests throughout the area of an alert make preparations to protect life and property, and do not disregard it on the strength of the detailed forecast track. Tropical cyclones are not points, and forecasting their track remains an uncertain science.
==Western hemisphere==
In conjunction with the National Hurricane Center, the national meteorological and hydrological services of Central America and the northern Atlantic Ocean, excluding mainland Africa and Europe, all issue tropical storm/hurricane watches and warnings. Tropical storm watches are issued when gale and storm force winds of between 34–63 knots (39–73 mph; 63–118 km/h) are possible, within 48 hours in a specified area in association with a tropical, subtropical or post-tropical cyclone. These watches are upgraded to tropical storm warnings, when gale and storm force winds become expected to occur somewhere in the warning area within 36 hours.〔 Hurricane watches are issued when sustained winds of are possible, within 48 hours in a specified area in association with a tropical, subtropical or post-tropical cyclone.〔 These warnings are upgraded to hurricane warnings, when hurricane force winds become expected to occur somewhere in the warning area within 36 hours.〔
Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch and warnings are issued in advance of the anticipated onset of tropical-storm-force winds, rather than in advance of the anticipated onset of hurricane-force winds.〔 At times a tropical storm warning and a hurricane watch can both be in effect due to uncertainties in the forecast. These watches and warnings are also issued by the Central Pacific Hurricane Center for the Hawaiian Islands and the Weather Forecast Office in Guam for parts of Micronesia but not for American Samoa due to an international agreement.
Within the United States an extreme wind warning is issued by the National Weather Service for any land areas that are expected to be impacted by a category 3 or higher hurricane and by sustained surface winds greater than or equal to 100 knots (115 mph; 185 km/h).〔 all landfalling hurricane is expected to bring winds of 100 knots (115 mph, 185 km/h, 51 m/s) to a specific location. The warning is issued just prior to when the strongest winds of the eyewall are expected to impact an area.〔(【引用サイトリンク】title=Product Description Document: Extreme Wind Warning (EWW) )〕 The warning is to be issued for the smallest area possible, and be valid for times of two hours or less.〔 It was developed in response to confusion resulting from the landfall of Hurricane Katrina. NWS offices in Jackson and New Orleans/Baton Rouge issued 11 tornado warnings for areas that would not experience an actual tornado, but would experience extreme wind speeds commonly associated with tornadoes.〔(【引用サイトリンク】title=Service Assessment. Hurricane Katrina: August 23–31, 2005 )〕 The extreme wind warning is now expected to be used in these situations.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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