Tropical cyclone warnings and watches

 

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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.

North Atlantic systems

See also: History of Atlantic hurricane warnings

The following terminology used by the US National Hurricane Center is the model for countries around the North Atlantic and in the Caribbean basin. This is also used for the Pacific coasts of Mexico, Central America, southern California, and Hawaii. The timing and naming of tropical cyclone advisories, watches, and warnings has changed over time. In 1958, tropical cyclone advisories were issued every six hours starting at 0400 UTC each day. During 1967, hurricane watches were used to designate areas where hurricane conditions were possible in the next 24 hours, while hurricane warnings indicated areas where the hurricane center should cross the coast. Small craft, gale, and storm warnings were issued for hurricanes not expected to make landfall. By 1987, the definition of tropical cyclone watches had changed to areas where gale or hurricane-force winds were possible within 36 hours, with warnings issued when gale or hurricane-force winds were expected within 24 hours. In 1987, gale watches/warnings were renamed tropical storm watches/warnings. In 1991, advisory timing shifted back to every six hours starting at 0330 UTC every day. In 1992, advisory timing changed to every six hours starting at 0300 UTC each day. The length of time used for watches and warnings changed again in 2010, with watches using a 48 hour time frame and warnings using a 36 hour time frame.

Tropical storms

Tropical Storm Watch

A tropical storm watch (TRA) is issued when tropical storm conditions, including winds from 39 to 73 mph (35 to 64 knots, 63 to 117 km/h) pose a possible threat to a specified coastal area within 48 hours. Maritime flags indicate this with a single square red flag.

Tropical Storm Warning

A tropical storm warning (TRW) is issued when tropical storm conditions (as above) are expected in a specified coastal area within 36 hours or less. Maritime flags indicate this with a single square red flag with a black square in the middle.

Tropical storm warning flag

Hurricanes

Hurricane Watch

A hurricane watch (HUA) is issued when the onset of tropical storm conditions appear possible in the warning area within the next 48 hours. Maritime flags indicate this with two square red flags.

The purpose of a hurricane watch is to inform families to obtain supplies, secure their homes, and be prepared to evacuate.

Hurricane Warning

Hurricane warning flags (USA)

A hurricane warning (HUW) is issued when a hurricane with sustained winds of 74 mph (65 knots, 118 km/h) or higher is expected. The National Hurricane Center will issue the HUW when tropical storm conditions are likely in the warned area within the next 36 hours. Maritime flags indicate this with two square red flags with a black square in the middle of each.

A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continues, even though the winds may have subsided below hurricane intensity.

Where the intensity or track of a forecast cyclone are uncertain (such as a tropical storm bordering hurricane intensity or on the edge of a track), a Tropical Storm Warning and a Hurricane Watch are often in effect at the same time on parts of the coast. Maritime flags indicate this with two square red flags with a black square in the middle on only one of them.

Major Hurricanes

Extreme Wind Warning

Extreme wind warnings are issued for any land areas that are in the path of a landfalling category 3 or higher (major) hurricane that are expected to see 115 mph or greater winds, usually associated with the eyewall. (This warning type was created after Hurricane Katrina when several tornado warnings were issued due to the extreme winds, but no actual tornadoes occurred or were forecast to occur.)

Deprecated Inland advisories

The following alerts were issued for inland areas that might have seen tropical storm or hurricane force wind and/or rain conditions, but were not located along the coast prior to 2011. These started appearing in the 2000s, originally with the word "Wind" inserted before the "Watch" or "Warning", which was dropped for 2005. All appeared to be issued with Specific Area Message Encoding event codes HWA and HWW, used for high wind watches and warnings, though they may have later come to be under the same codes as regular tropical cyclone advisories. Previously, standard High Wind Warnings and Watches were issued (which denote >=39 MPH winds or >=58 MPH gusts). When they were inland, watches and/or warnings were posted for tropical storm or hurricane force winds in the next 24 hours or so. In 2011, these alerts became deprecated in favor of issuing a unified coastal/inland warning. The coastal strip is determined by the NHC, and the Local WFOs determine the inland portion of the warning. Below are the deprecated watches and warnings.

Inland Tropical Storm Watch (deprecated)

Formerly issued for inland areas where sustained winds of 39 to 73 mph (62 to 117 km/h) associated with a tropical storm were anticipated beyond the coastal areas though the actual occurrence, timing and location are still uncertain.

Inland Tropical Storm Warning (deprecated)

Formerly issued for inland counties where tropical storm conditions were anticipated beyond the coastal areas in the next six to twelve hours.

Inland Hurricane Watch (deprecated)

Formerly issued for inland counties where sustained winds of 74 mph (118 km/h) or greater associated with a hurricane were anticipated beyond the coastal areas though the actual occurrence, timing and location are still uncertain.

Inland Hurricane Warning (deprecated)

Formerly issued for inland counties where sustained hurricane force winds were anticipated beyond the coastal areas in the next six to twelve hours.

Other advisories

Other advisories are also commonly issued in association with tropical cyclones, but are not specific to them.

• Tropical cyclones often produce tornadoes, prompting the issuing of tornado watches and warnings.
• A Wind Advisory/small craft advisory is issued for less severe wind conditions (either at the edges of the storm or after significant weakening) that are strong (at least 25 mph/40 km/h) but sustained below tropical storm force.
• Heavy rains associated with tropical systems often result in flood watches and warnings.
• If a tropical storm warning or hurricane warning is not in effect for an area which is expected to experience storm surge, a coastal flood warning will be issued for that area.
• If a storm becomes extratropical or degenerates into a wave or low but retains winds of at least tropical storm force, a high wind warning would be issued for inland areas and a gale warning, storm warning or hurricane force wind warning would be issued for marine areas.

Regional notes

Before the 2004 Atlantic hurricane season, these warnings were not issued in Canada (who simply issued standard wind and rain warnings, which are now issued alongside the NHC-standard warnings). That policy was changed when it appeared that the population did not realize the dangers from four storms in 2003 that affected different land and offshore areas of Canada, the worst of which was Hurricane Juan in Nova Scotia, even if regular warning bulletins were issued well in advance. The inland watches and warnings are not differentiated from the coastal watches and warnings in Canada; the hurricane and tropical storm watches and warnings can be issued for any forecast area.

In Cuba, warnings are issued by province, not by coastal location or breakpoints. There are no differentials between coastal and inland warnings there as they are automatically issued for both types of areas.

A similar system was implemented in 2011 in the United States. NHC-issued breakpoints are used as guidance and indicate the marine warnings in the area, and the local WFOs expand the warning to include affected inland areas. The expanded warning area is issued by counties, rather than areas as large as Cuban provinces.

West Pacific systems

China

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

• Warning: Winds may reach Beaufort Force 8 or rainstorm may occur in 48 hours.
• Urgent Warning: Winds may reach Beaufort Force 8 or rainstorm may occur in 24 hours.

Nowadays, the use of this system is restricted to coastal waters only. Thus, warnings may be discontinued even the cyclone is maintaining tropical storm intensity inland. However, color-coded alerts (mentioned below) may be in effect.

Guangdong introduced a color-coded tropical cyclone warning system for land use in 2000.

• White alert: A tropical cyclone may affect the area in 48 hours.
• Green alert: Winds may reach Beaufort Force 6 in 24 hours or winds of Beaufort Force 6~7 are already blowing.
• Yellow alert: Winds may reach Beaufort Force 8 in 12 hours or winds of Beaufort Force 8~9 (gale force) are already blowing.
• Red alert: Winds may reach Beaufort Force 10 in 12 hours or winds of Beaufort Force 10~11 (storm force) are already blowing.
• Black alert: Winds may reach Beaufort Force 12 in 12 hours or winds of Beaufort Force 12 (hurricane force) are already blowing.

Similar systems were developed in Fujian and Shanghai.

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.

• Blue alert: Winds may reach Beaufort Force 6 in 24 hours or winds of Beaufort Force 6~7 are already blowing.
• Yellow alert: Winds may reach Beaufort Force 8 in 24 hours or winds of Beaufort Force 8~9 (gale force) are already blowing.
• Orange alert: Winds may reach Beaufort Force 10 in 12 hours or winds of Beaufort Force 10~11 (storm force) are already blowing.
• Red alert: Winds may reach Beaufort Force 12 in 6 hours or winds of Beaufort Force 12 (hurricane force) are already blowing.

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

Pearl River Delta

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 approximate location of a tropical cyclone from Hong Kong. The Macao Meteorological and Geophysical Bureau in Macau uses a similar system.

Okinawa

A multi-stage system called the Tropical Cyclone Condition of Readiness (TCCOR), is used for the United States military base and residents on Okinawa, Japan. Each stage relates to a level of preparation that is recommended to be undertaken before a storm arrives. Between June 1 and November 30, TCCOR 4 is constantly in effect. TCCOR 1 is broken into four different situation levels based on current conditions.

• TCCOR 4 – Destructive winds of 57 mph (50 kt, 93 km/h) or greater are possible within 72 hours.
  • Now is the time to stock-up on food and Typhoon Supplies.
• TCCOR 3 – Destructive winds of 57 mph (50 kt, 93 km/h) or greater are possible within 48 hours.
  • Initiate a general cleanup around homes and office.
• TCCOR 2 – Destructive winds of 57 mph (50 kt, 93 km/h) or greater are anticipated within 24 hours.
  • Remove or secure all outside items.
• TCCOR 1 – Destructive winds of 57 mph (50 kt, 93 km/h) or greater are anticipated within 12 hours.
  • No school for Department of Defense District School (DoDDS) students. Staff and teachers will work normal hours, unless changed by DoDDS superintendent. Fill any containers you can use for water storage. If you live in low lying quarters, make arrangements to stay with a friend. Make final check of food and other supplies.
• TCCOR 1 Caution – Destructive winds of 57 mph (50 kt, 93 km/h) or greater are anticipated within 12 hours. Actual winds are 39 to 56 mph (34 to 49 knots, 63 to 91 km/h).
  • All nonessential personnel will be released to their quarters at this time. DoDDS schools will close at this time. Staff and teachers return home or remain home. Base exchange, shops, Commissary, Shoppettes, Gas Station, Services facilities, Clubs, Restaurants, Recreational Facilities and Post Office will close. Movement about the base should be kept to a minimum. SFS will enforce "essential vehicles only"policy.
• TCCOR 1 Emergency – Actual winds of 57 mph (50 kt, 93 km/h) or greater are occurring.
  • All outside activity is prohibited.
• TCCOR 1 Recovery – Destructive winds of 57 mph (50 kt, 93 km/h) or greater are no longer occurring. Actual winds are 39 to 56 mph (34 to 49 knots, 63 to 91 km/h).
  • Nonessential functions remain closed unless directed by the commander. All but emergency essential personnel remain in their quarters.
• Storm Watch – The typhoon is moving away but the base is still feeling some effects. Hazardous conditions may exist due to storm damage. In some cases the storm could return to Okinawa, so stay alert.
  • All military and civilian personnel will return to work within 2 hours or at normal duty hours unless otherwise instructed by their commander. The Commissary and BX will resume operations, unless directed otherwise by the installation commander.
• All Clear – Hazardous conditions and winds are no longer present. Return to normal duties. All Clear is announced when all hazards have been cleared.
  • DoDDS teachers, staff and students will return to school during normal hours. From June 1 to November 30 Okinawa will return to TCCOR 4.

Philippines

Signal #1 winds of 30–60 km/h (20-35 mph) are expected to occur within 36 hours

Signal #2 winds of 60–100 km/h (40-65 mph) are expected to occur within 24 hours

Signal #3 winds of 100–185 km/h, (65-115 mph) are expected to occur within 18 hours.

Signal #4 winds of at least 185 km/h, (115 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). An area having a storm signal may be under:

• PSWS #1 - Tropical cyclone winds of 30–60 km/h are expected within the next 36 hours. (Note: If a tropical cyclone forms very close to the area, then a shorter lead time is seen on the warning bulletin.)
• PSWS #2 - Tropical cyclone winds of 60–100 km/h are expected within the next 24 hours.
• PSWS #3 - Tropical cyclone winds of 100–185 km/h are expected within the next 18 hours.
• PSWS #4 - Tropical cyclone winds of greater than 185 km/h are expected within 12 hours.

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 nearer and nearer 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 to an area, it may be downgraded to a lower signal or may be lifted (that is, an area will have no storm signal).

See also

• Gale warning
• HURCON
• iTyphoon – A mobile application used to provide information about typhoons in the Philippines.
• Severe weather terminology
• Small craft advisory
• Storm warning
• Tropical cyclone

External links

• NHC - watches and warnings