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.
See also: History of Atlantic hurricane warnings. 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.[1] [2] [3] [4] [5] 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.[6] Tropical storm watches are issued when gale and storm force winds of between 34 and 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.[7] 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.[7] Hurricane watches are issued when sustained winds of 64kn are possible, within 48 hours in a specified area in association with a tropical, subtropical or post-tropical cyclone.[7] These watches are upgraded to hurricane warnings, when hurricane-force winds become expected to occur somewhere in the warning area within 36 hours.[7]
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.[7] 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.[8]
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 (Category 3 or higher) hurricane and by sustained surface winds greater than or equal to 100 knots (115 mph; 185 km/h).[8] The warning is issued just prior to when the strongest winds of the eyewall are expected to impact an area.[9] 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.[10] 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.[11]
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.[12]
In Canada, terminology is fairly similar to that of the United States, but there are a few differences:[13]
A two-stage warning system was long-established in China for tropical cyclones of tropical storm intensity of above.[14] 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 (below) may be in effect independently of any two-stage warnings.
Later, China Meteorological Administration standardized the system for national use.[15] 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 (such as Qinghai, etc.), 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:[16]
| Name | Meaning | |
|---|---|---|
| Windproof Info (Tropical Storm or Typhoon Info) | indicates that a tropical storm or typhoon has entered the South China Sea (or has formed in the South China Sea) and is likely to move to the coastal areas of the province. | |
| Windproof Warning (Tropical Storm and Typhoon 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 (Tropical Storm or Typhoon Emergency 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 (Tropical Storm or Typhoon Disarming Alert) | indicates that a tropical storm or typhoon has landed (or weakened to a low pressure). |
| 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 (6-7) (41-62 km/h). | ||
| Yellow typhoon alert | Tropical cyclones will be within 12 hours or are affecting the area, with an average winds level of strong gale (8-9) (63-87 km/h). | ||
| Red typhoon alert | Tropical cyclones will be within 12 hours or are affecting the area, with an average winds level of strong storm (10-11) (88-117 km/h). | ||
| Black typhoon alert | Tropical cyclones will be within 12 hours or are affecting the area, with an average winds level of typhoon (>12). |
| 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. |
| 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. |
Shenzhen currently uses a different signal from Guangdong Province:[18] [20]
Zhuhai adopts the signal style of Guangdong Province, but the meaning of the signal is different:[21]
Shenzhen and Zhuhai used digitally arranged typhoon signals from June 4, 1994, to November 1, 2000,[22] but they have now been replaced by typhoon warning signals.
The coastal ports of various cities in mainland China will still hang the squash signal when the typhoon hits.[23] The sign is roughly the same as the typhoon signal used in Shenzhen and Zhuhai.
See main article: Hong Kong tropical cyclone warning signals.
The Pearl River Delta uses a variety of warning systems to inform the public regarding the risks of tropical cyclones to the area.
The Hong Kong Observatory issues typhoon signals to indicate the existence and effects of a tropical cyclone on Hong Kong. The first numeric warning system was used in 1917.
The Macao Meteorological and Geophysical Bureau in Macau uses a similar system.[24]
In Hong Kong the typhoon signal system consists of 8 signals in 5 levels numbered non-consecutively for historical reasons.[25] [26] Each signal has a day signal and a night signal for hoisting, which are still hoisted in Macau but no longer hoisted in Hong Kong. Day signals are also used as signal symbols in both places.
See main article: Japan Meteorological Agency. The Japan Meteorological Agency (JMA) is the government agency responsible for gathering and providing results for the public in Japan, that are obtained from data based on daily scientific observation and research into natural phenomena in the fields of meteorology, hydrology, seismology and volcanology, among other related scientific fields. Its headquarters is located in Tokyo.
JMA is also designated one of the Regional Specialized Meteorological Centers (RSMC) of the World Meteorological Organization. It has the responsibility for weather forecasting, tropical cyclone naming and distribution of warnings for tropical cyclones in the Northwestern Pacific region.
PhilippinesSee main article: Tropical Cyclone Wind Signals. The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) releases tropical cyclone warnings in the form of Tropical Cyclone Wind Signals (TCWS, or "wind signals").[27] Within this warning system, an area having a wind signal may be under:
These wind signals are hoisted when an area (in the Philippines only) is about to be directly affected by tropical cyclone winds. Wind signals for specific areas can be escalated to higher signal levels (and the lead times shortened consequently) as a tropical cyclone gains strength and/or gets closer to the areas about to be affected. De-escalation and/or lifting of wind signals are implemented once a tropical cyclone weakens and/or gets farther away from the affected areas. The lead time is also only valid for the first issuance.
Vietnam recognises its typhoon season from the beginning of June through to the end of November,[28] with an average of four to six typhoons hitting the country annually.[29] Any tropical cyclones here are monitored by the National Center for Hydro-Meteorological Forecasting (NCHMF), which is the nation's official meteorological agency and was established in January 2003. The NCHMF tracks a storm should it enter the agency's monitoring area range which is within the East Sea to the west of 120°E and north of 5°N. Any storm that enters this area is assigned a number, and is set according to its sequence of its occurrence – as for instance with Bão số 1 etc., which translates to "Storm no. 1". Bão comes from "暴', meaning ferocious, violent or vicious, but in vernacular Vietnamese has come to mean "storm".
In 2014, the Vietnamese government issued Decree no.44/2014, introduced five warning levels, but NCHMF only use three out of five levels to issue typhoon warnings:
- "Disaster Risk Alert - Level 3" (High Alert), decorated with orange
- "Disaster Risk Alert - Level 4" (Very High Alert), decorated with red
- "Disaster Risk Alert - Level 5" (Disaster Alert), decorated with pink
The Australian Bureau of Meteorology will issue a cyclone watch for a specified part of Australia, when a tropical cyclone is expected to cause gale-force winds in excess of 62round=5NaNround=5 within 24–48 hours and subsequently make landfall.[30] A cyclone warning is subsequently issued for a specified part of Australia when a tropical cyclone, is expected to cause or is causing gale-force winds in excess of 62round=5NaNround=5 within 24 hours and is subsequently expected to make landfall.[30]
The Fiji Meteorological Service (FMS) issues a tropical cyclone alert for the Cook Islands, Fiji, Kiribati, Nauru, Niue, Tokelau and Tuvalu, when a tropical cyclone has a significant probability of causing gale-force winds or stronger winds within 24–48 hours. Gale, storm and hurricane-force wind warnings are subsequently issued for the above areas by FMS, when a tropical cyclone is either causing or expected to cause either gale storm or hurricane-force winds within 24 hours.
Météo-France is responsible for the issuance of tropical cyclone watches and warnings for New Caledonia, Wallis and Futuna, French Polynesia and the Pitcairn Islands. The National Meteorological and Hydrological Services of the Solomon Islands, Samoa, Indonesia, Papua New Guinea, Tonga, New Zealand, Vanuatu, Timor Leste and American Samoa are responsible for their own watches and warnings.
The Indian Meteorological Department (IMD/RSMC New Delhi) is responsible for tracking tropical cyclones within the North Indian Ocean.Météo-France in Réunion (MFR/RSMC La Reunion) is responsible for the issuing advisories and tracking of tropical cyclones in the southwest part of the basin, however, the naming of systems is deferred to the Mauritius and Madagascar weather services.
The IMD issues warnings in four stages for the Indian coast.
Cyclonic storm conditions mean what winds in excess of 63 km/h (39 mph) are possible.[31]
Mauritius Meteorological Services is responsible for naming tropical systems in the South-West Indian Ocean between 55°E and 90°E. They issue four different levels of cyclone warnings for the islands of Mauritius and Rodrigues.
Météo-France issues five levels of alerts for the French overseas department and region of Réunion.[33]
See main article: HURCON. The United States Department of Defense uses a multi-stage system called the Hurricane Condition (HURCON) in the North Atlantic and the Northeast Pacific and the Tropical Cyclone Condition of Readiness (TCCOR) in the western Pacific to prepare bases and evacuate assets and personnel in advance of adverse weather associated with tropical cyclones.[34]
The alerts are recommended by weather facilities either on base or by central sites like the National Hurricane Center or the Joint Typhoon Warning Center and are generally related to the timing and potential for destructive sustained windspeeds of above 50kn.[34] Recommendations are then considered by base or area commanders along with other subjective factors for setting the alert status like assets, holidays or the bases experience in emergency preparedness.[34] The bases prefer to set these alerts sequentially, from HURCON or TCCOR 5 with destructive winds expected within 96 hours, through levels 4, 3, 2 and if needed to a series of four different level 1 conditions, however depending on the cyclone's movement or location some of these signals can be skipped.[34] [35] After a system passes and stops affecting the base, the authorities can decide to revert to the lowest level or stay in a heightened approach if another tropical cyclone is approaching.[34]