Tropical cyclone warnings and watches
Tropical cyclone warnings and watches are alerts 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.
Western Hemisphere
New tropical cyclone position and forecast information is available at least every twelve hours in the Southern Hemisphere and at least every six hours in the Northern Hemisphere from Regional Specialized Meteorological Centers and Tropical Cyclone Warning Centers.In conjunction with the National Hurricane Center, the national meteorological and hydrological services of Central America, the northern Atlantic Ocean, and the northeastern Pacific Ocean east of the 140th meridian west, 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 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 watches 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 major hurricane and by sustained surface winds greater than or equal to. The warning is issued just prior to when the strongest winds of the eyewall are expected to impact an area. 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. The extreme wind warning is now expected to be used in these situations.
In 2017, the National Hurricane Center introduced a new system of warnings and watches for storm surge, which would cover the Atlantic and Gulf Coasts of the United States. A storm surge watch would be issued when a life-threatening storm surge, associated with a potential or ongoing tropical, subtropical or post-tropical cyclone, is possible within the next 48 hours. These watches would be upgraded to storm surge warnings when there is a danger of life-threatening storm surge occurring within 36 hours. However, both watches and warnings may be issued earlier than specified if environmental conditions are expected to hamper preparations.
In Mexico, a color coded alert system is used to keep the public informed when a tropical cyclone or possible tropical cyclones poses a threat to the nation. The scale starts with blue at the bottom being minimal danger, then proceeds to a green alert, which means low level danger. A yellow alert signifies moderate danger, followed by an orange alert that means high danger level. The scale tops off with a red alert, the maximum level of danger.
Canada
In Canada, terminology is fairly similar to that of the United States, but there are a few differences:- Watches are issued 36 hours prior to a tropical cyclone making landfall.
- Warnings are issued 24 hours prior to the tropical cyclone making landfall.
- If sustained winds 70 km/h and/or gusts 90 km/h or stronger are predicted, a conventional wind warning will be issued along with the tropical cyclone watches and warnings.
- A storm surge warning may be issued if abnormally high water levels are predicted.
Western Pacific basin
China
A two-stage warning system was long-established in China for tropical cyclones of tropical storm intensity of above. Nowadays, the use of this system is restricted to coastal waters only. Thus, warnings may be discontinued even if a cyclone is maintaining tropical storm intensity inland. Color-coded alerts may be in effect independently of any two-stage warnings.Later, China Meteorological Administration standardized the system for national use. This set is part of a larger warning system that covers other forms of severe weather conditions, such as extreme temperature, torrential rainfall, drought, etc.
| Level | Name | Sign | Meaning |
| IV | Blue typhoon alert 台风蓝色预警信号 | Within 24 hours, it may or may have been affected by tropical cyclones. The average wind power on the coast or land is above 6, or the gust above 8 and may continue. | |
| III | Yellow typhoon alert 台风黄色预警信号 | Within 24 hours, it may or may have been affected by tropical cyclones. The average wind power on the coast or land is above 8, or the gust above 10 and may continue. | |
| II | Orange typhoon alert 台风橙色预警信号 | Within 12 hours, it may or may have been affected by tropical cyclones. The average wind power on the coast or land is above 10, or the gust above 12 and may continue. | |
| I | Red typhoon alert 台风红色预警信号 | Within 6 hours, it may or may have been affected by tropical cyclones. The average wind power on the coast or land is above 12, or the gust above 14 and may continue. |
Guangdong
continued to set up the White typhoon alert for typhoon, indicating that tropical cyclones may affect the area within 48 hours. In some inland areas that are less affected by tropical cyclones, there is no typhoon warning signal, but when it is hit by tropical cyclones, a strong wind warning signal will be issued. The winds represented by each color are consistent with the typhoon warning signal.Typhoon warning signals used in Guangzhou from June 1, 1995, to November 1, 2000:
| Name | Meaning |
| Windproof Info | indicates that a tropical storm or typhoon has entered the South China Sea and is likely to move to the coastal areas of the province. |
| Windproof Warning | Indicating that a tropical storm or typhoon warning enters the South China Sea, its route is moving in the direction of the Pearl River Estuary. If there is no change, it may land within 48 hours. |
| Windproof Special Alert | Indicating that a tropical storm or typhoon hits the Pearl River Estuary within 24 hours, or landed in a coastal area within 150 kilometers of the Pearl River Estuary, which will have a serious impact on Guangzhou. |
| Disarming | indicates that a tropical storm or typhoon has landed. |
Typhoon warning signals used from November 1, 2000, to May 2006:
| Name | Signal | Meaning |
| White typhoon alert | Tropical cyclones may affect the area within 48 hours. | |
| Green typhoon alert | Tropical cyclones will be within 24 hours or are affecting the area, with an average wind level of strong winds . | |
| Yellow typhoon alert | Tropical cyclones will be within 12 hours or are affecting the area, with an average winds level of strong gale . | |
| Red typhoon alert | Tropical cyclones will be within 12 hours or are affecting the area, with an average winds level of strong storm . | |
| Black typhoon alert | Tropical cyclones will be within 12 hours or are affecting the area, with an average winds level of typhoon. |
Typhoon warning signals used from June 1, 2006, to December 31, 2014:
| Name | Signal | Meaning |
| White typhoon alert | Tropical cyclones may affect the area within 48 hours. | |
| Blue typhoon alert | It may be affected by tropical cyclones within 24 hours, the average wind power can reach above level 6, or gusts above 7; or it has been affected by tropical cyclones with an average wind power of 6–7, or gusts of 7–8, and may continue. | |
| Yellow typhoon alert | It may be affected by tropical cyclones within 24 hours, the average wind power can reach above level 8, or gusts above 9; or it has been affected by tropical cyclones with an average wind power of 8–9, or gusts of 9–10, and may continue. | |
| Orange typhoon alert | It may be affected by tropical cyclones within 12 hours, the average wind power can reach above level 10, or gusts above 11; or it has been affected by tropical cyclones with an average wind power of 10–11, or gusts of 11–12, and may continue. | |
| Red typhoon alert | It may be affected by tropical cyclones within 6 hours, the average wind power can reach above level 12; or it has been affected by tropical cyclones with an average wind power of 12, and may continue. |
Typhoon warning signals used since January 1, 2015:
| Name | Signal | Meaning |
| White typhoon alert | Tropical cyclones may affect the area within 48 hours. | |
| Blue typhoon alert | It may be affected by tropical cyclones within 24 hours, the average wind power can reach above level 6, or gusts above 7; or it has been affected by tropical cyclones with an average wind power of 6–7, or gusts of 7–8, and may continue. | |
| Yellow typhoon alert | It may be affected by tropical cyclones within 24 hours, the average wind power can reach above level 8, or gusts above 9; or it has been affected by tropical cyclones with an average wind power of 8–9, or gusts of 9–10, and may continue. | |
| Orange typhoon alert | It may be affected by tropical cyclones within 12 hours, the average wind power can reach above level 10, or gusts above 11; or it has been affected by tropical cyclones with an average wind power of 10–11, or gusts of 11–12, and may continue. | |
| Red typhoon alert | It may be affected by tropical cyclones within 6 hours, the average wind power can reach above level 12; or it has been affected by tropical cyclones with an average wind power of 12, and may continue. |