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

General
Hurricane Warning
Hurricane conditions
expected within 36 hours.
Hurricane Watch
Hurricane conditions
possible within 48 hours.
Tropical Storm Warning
Tropical storm conditions expected within 36 hours.
Tropical Storm Watch
Tropical storm conditions possible within 48 hours.
Storm surge
Storm Surge Warning
Life-threatening inundation from storm surge possible within 36 hours.
Storm Surge Watch
Life-threatening inundation from storm surge possible within 48 hours.

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 34–63 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 64 knots (74 mph; 119 km/h) are possible, within 48 hours in a specified area in association with a tropical, subtropical or post-tropical cyclone.[7] These warnings 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.[9] 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]

West Pacific systems

China

A two-stage warning system was long-established in China for tropical cyclones of tropical storm intensity of above.[13] 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.

Guangdong introduced a color-coded tropical cyclone warning system for land use in 1999.[14]

Similar systems were developed in Fujian and Shanghai.

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. Guangdong maintained a white alert as in the old system.

Hong Kong and Macau

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 Macao Meteorological and Geophysical Bureau in Macau uses a similar system. [16]The signal system consists of 8 signals in 5 levels numbered non-consecutively for historical reasons. [17][18] 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.

Japan

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.

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.

Philippines

Signal #1
winds of 30–60 km/h (20-37 mph) are expected to occur within 36 hours
Signal #2
winds of 61–120 km/h (38–73 mph) are expected to occur within 24 hours
Signal #3
winds of 121–170 km/h, (74–105 mph) are expected to occur within 18 hours.
Signal #4
winds of 171–220 km/h, (106–137 mph) are expected to occur within 12 hours.
Signal #5
winds of at least 220 km/h, (137 mph) are expected to occur within 12 hours.

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) releases tropical cyclone warnings in the form of Public Storm Warning Signals (or just storm signals).[19] An area having a storm signal may be under:

These storm signals are usually heightened when an area (in the Philippines only) is about to be hit by a tropical cyclone. Thus, as a tropical cyclone gains strength and/or gets closer to an area having a storm signal, it may be heightened to another higher signal in that particular area. Whereas, as a tropical cyclone weakens and/or gets farther away from an area, it may be downgraded to a lower signal or may be lifted (that is, an area will have no storm signal).

South Pacific basin

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 62 km/h (40 mph) within 24–48 hours and subsequently make landfall.[20] 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 62 km/h (40 mph) within 24 hours and is subsequently expected to make landfall.[20]

The Fiji Meteorological Service (FMS) issues a tropical cyclone alert for the Cook Islands, Fiji, Kiribati, Nauru, Niue, Tokelau, Tonga and Tuvalu, when a tropical cyclone has a significant probability of causing gale-force winds or stronger winds within 24–48 hours.[21] 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.[21]

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.[21] The National Meteorological and Hydrological Services of the Solomon Islands, Samoa, Indonesia, Papua New Guinea, New Zealand, Timor Leste and American Samoa are responsible for their own watches and warnings.[21]

Indian Ocean systems

The India 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.

India

Cyclone Watch
Cyclonic storm conditions possible within 72 hours.
Cyclone Alert
Cyclonic storm conditions possible within 48 hours.
Cyclone Warning
Cyclonic storm conditions expected within 24 hours.
Landfall Outlook
Cyclonic storm conditions expected within 12 hours.

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.[22]

Military advisories

Tropical Cyclone Condition of Readiness

The United States Department of Defense uses a multi-stage system called the Tropical Cyclone Condition of Readiness (TC-CORs) otherwise known as the Hurricane Condition of Readiness (HURCONs), to prepare bases and evacuate assets and personnel in advance of adverse weather associated with tropical cyclones.[23]

TC-COR Hours Notes
5 96 This is set by military bases in the US, throughout the Atlantic hurricane season.
4 72 Guam is in TC-COR 4 throughout the year, while Japanese bases set this from June 1 - November 30.
3 48 Destructive winds are possible within 48 hours.
2 24 Destructive winds are now expected within 24 hours.
1 12 Destructive winds are now expected within 12 hours, but gale force winds are not yet occurring.
1C 12 Gale-force winds are occurring.
1E 0 Winds of above 50 kn (58 mph; 93 km/h) are occurring.
1R Winds of above 50 kn (58 mph; 93 km/h) are no longer occurring, but gale-force winds are occurring.
Storm Watch The system is moving away but the base is still feeling some effects.
All-Clear Revert to seasonal TC-COR

TC-CORs 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 50 kn (58 mph; 93 km/h).[23] Recommendations are then considered by base or area commanders along with other subjective factors for setting the TC-CORs like assets, holidays or the bases experience in emergency preparedness.[23] The bases prefer to set these TC-CORs sequentially, from TC-COR 5 with destructive winds expected within 96 hours, through TC-COR 4, 3, 2 and if needed to a series of four different TC-COR 1 conditions, however depending on the cyclone's movement or location some of these signals can be skipped.[23][24] After a system passes and stops affecting the base, the authorities can decide to revert to the seasonal TC-COR or stay in a heightened approach as another tropical cyclone is approaching.[23]

See also

References

  1. ↑ "Regional Specialized Meteorological Center". Tropical Cyclone Program (TCP). World Meteorological Organization. April 25, 2006. Retrieved November 5, 2006.
  2. ↑ Fiji Meteorological Service (2017). "Services". Retrieved 2017-06-04.
  3. ↑ Joint Typhoon Warning Center (2017). "Products and Service Notice". United States Navy. Retrieved 2017-06-04.
  4. ↑ National Hurricane Center (March 2016). "National Hurricane Center Product Description Document: A User's Guide to Hurricane Products" (PDF). National Oceanic and Atmospheric Administration. Retrieved 2017-06-03.
  5. ↑ Japan Meteorological Agency (2017). "Notes on RSMC Tropical Cyclone Information". Retrieved 2017-06-04.
  6. ↑ RA IV Hurricane Committee (May 30, 2013). Hurricane Operational Plan (PDF) (Technical Document). World Meteorological Organization. Archived (PDF) from the original on December 16, 2013. Retrieved December 15, 2013.
  7. 1 2 3 4 5 "Glossary of NHC Terms". United States National Oceanic and Atmospheric Administration's National Weather Service. March 25, 2013. Archived from the original on December 16, 2013. Retrieved December 15, 2013.
  8. 1 2 Tropical Cyclone Products (PDF) (National Weather Service Instruction 10-601). United States National Oceanic and Atmospheric Administration's National Weather Service. June 11, 2013. pp. 4–9, 56. Archived (PDF) from the original on December 16, 2013. Retrieved December 15, 2013.
  9. 1 2 National Weather Service. "Product Description Document: Extreme Wind Warning (EWW)" (PDF). Retrieved 2007-10-04.
  10. ↑ U.S. Department of Commerce. "Service Assessment. Hurricane Katrina: August 23–31, 2005" (PDF). Retrieved 2007-10-04.
  11. ↑ Storm surge watch & warning to become operational in 2017 (pdf) (Report). United States National Oceanic and Atmospheric Administration's National Weather Service. January 23, 2017. Retrieved January 26, 2017.
  12. ↑ "Be Prepared for Hurricane Season in Cancun". Royal Sunset. October 22, 2013. Retrieved August 15, 2016.
  13. ↑ Typhoon.gov.cn Archived August 30, 2006, at the Wayback Machine.
  14. ↑ Archived May 22, 2006, at the Wayback Machine.
  15. ↑ CMA.gov.cn Archived August 22, 2006, at the Wayback Machine.
  16. ↑ "Meaning of Tropical Cyclone Signals and the relevant recommended safety precautions". Macao Meteorological and Geophysical Bureau. Retrieved 10 April 2017.
  17. ↑ John YK Leung and WH Lui (9 August 2012). "Tropical Cyclone Warning Signal No.5 in the Past". Hong Kong Observatory. Retrieved 10 April 2017.
  18. ↑ "History of the Hong Kong Tropical Cyclone Warning Signals". Hong Kong Observatory. Retrieved 10 April 2017.
  19. ↑ "The Modified Philippine Public Storm Warning Signals". Kidlat.pagasa.dost.gov.ph. Archived from the original on 2012-02-02. Retrieved 2012-01-03.
  20. 1 2 "Tropical Cyclone Warning Advice". Australian Bureau of Meteorology. Retrieved December 15, 2013.
  21. 1 2 3 4 RA V Tropical Cyclone Committee (December 12, 2012). Tropical Cyclone Operational Plan for the South-East Indian Ocean and the Southern Pacific Ocean 2012 (PDF) (Report). World Meteorological Organization. pp. 7–13. Archived (PDF) from the original on April 1, 2013. Retrieved December 15, 2013.
  22. ↑ "Four Stage Warning". India Meteorological Department. Retrieved 23 October 2016.
  23. 1 2 3 4 5 Sampson, Charles R; Schumacher, Andrea B; Knaff, John A; DeMaria, Mark; Fukada, Edward M; Sisko, Chris A; Roberts, David P; Winters, Katherine A; Wilson, Harold M. "Objective Guidance for Use in Setting Tropical Cyclone Conditions of Readiness". Weather and Forecasting. 27 (4): 1052–1060. doi:10.1175/WAF-D-12-00008.1.
  24. ↑ Fleet Weather Center (February 8, 2013). "Tropical Cyclone Quick Reference Guide 2013" (PDF). United States Navy. p. 2. Retrieved December 15, 2013.
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