Tropical Cyclone Wind Signals

File:Tropical Cyclone Wind Signals due to Typhoon Noru, 5 PM PhST, 25 September 2022.png|thumb|350px|Map of Tropical Cyclone Wind Signals hoisted due to Typhoon Noru at 5:00 PM PHT on September 25, 2022, covering most of Luzon in addition to some surrounding areas.
The Tropical Cyclone Wind Signals are tropical cyclone alert levels issued by the Philippine Atmospheric, Geophysical, and Astronomical Services Administration to areas within the Philippines that may be affected by tropical cyclone winds and their associated hazards.
PAGASA's TCWS system is activated when a tropical cyclone is inside or near the Philippine Area of Responsibility and is forecast to affect the Philippine archipelago. It is a tiered system with five numbered levels, with higher numbers associated with higher wind speeds and shorter "lead times", which are periods within which an expected range of wind strength is expected to occur. TCWS signals are issued for specific localities at the provincial or city/municipal level. They are escalated, de-escalated or lifted depending on the expected strength of winds and the movement of the tropical cyclone relative to the affected areas.
The TCWS system is the consequence of decades of evolution of early warning systems for tropical cyclones in the Philippines. The first tropical cyclone warning in the country was issued in July 1879. In 1931, the earliest formalized warning system for tropical cyclones was implemented by PAGASA's predecessor, the Philippine Weather Bureau. In the late 20th century, this system gradually became the more familiar four-tiered public storm warning signal system. It was subject to further revisions after the catastrophic onslaught of Typhoon Haiyan in 2013, which prompted the addition of a fifth warning level to emphasize extreme tropical cyclone winds. The current version of the TCWS was implemented in 2022.

Levels

Note: This table incorporates text from public domain sources authored by PAGASA.

Wind Signal No.	Wind speed	Warning lead time	Potential wind impacts	Corresponding tropical cyclone category
	Strong winds: Beaufort Force 6–7 39–61 km/h 22–33 kn 10.8–17.1 m/s 25–38 mph	36 hours	Minimal to minor threat to life and property House of poor construction, old dilapidated structures, and other structures made of light materials will suffer minimal to minor damage. Some banana and similar plants are tilted, while twigs of small trees may sway with the wind. Rice crops, especially those in flowering and ripening stages, may suffer some damage. Minimal disruption to public transportation	Tropical depressions and stronger
	Gale-force winds:Beaufort Force 8–9 62–88 km/h 34–47 kn 17.2–24.4 m/s 39–54 mph	24 hours	Minor to moderate threat to life and property Minor to moderate damage may occur to makeshift or old dilapidated structures, and other structures made of light materials. Houses of poor and average construction may receive minor roof damage. Unsecured, exposed lightweight items may become projectiles which may cause additional damage. Some electrical wires may be blown down, resulting in local power outages. Minor to moderate disruption to public transportation. Most banana and similar plants are tilted, with some stooped or downed. Some small trees blow over, with twigs and branches of frail trees broken. Considerable damage is likely to rice and other similar crops, especially those in flowering and ripening stages	Tropical storms and stronger
	Storm-force winds:Beaufort Force 10–11 89–117 km/h 48–63 kn 24.5–32.6 m/s 55–72 mph	18 hours	Moderate to significant threat to life and property Makeshift or old, dilapidated structures, and other structures made of light materials may suffer substantial damage. Houses of poor or average construction will have considerable roof damage, some blown-out windows, and/or partial wall damage. Well-constructed houses may suffer minimal to minor roof damage. Warehouses and other buildings in industrial parks may suffer minor to moderate damage. Unsecured, exposed outdoor items of light to moderate weight may become projectiles, causing additional damage or injuries. Many areas may suffer power outages with numerous downed power lines and posts. Minimal to minor disruption in telecommunications and potable water supply. Moderate to significant disruption to public transportation Some small trees, most banana and similar plants, and a few large trees are downed or broken. Rice and other similar crops, especially those in flowering and ripening stages may suffer heavy damage	Severe tropical storms and stronger
	Typhoon-force winds:Beaufort Force 12 118–184 km/h 64–99 kn 32.7–51.2 m/s 73–114 mph	12 hours	Significant to severe threat to life and property Severe damage will occur to makeshift or old, dilapidated of light structures, and other structures made of light materials. Houses of poor or average construction may receive major damage, including complete roof failure and possible wall collapse; a few may suffer severe damage. Most well-constructed houses may suffer minor to moderate roof damage, with some houses experiencing major roof failure; blown out windows are also likely. Failure of aluminum and steel roofs and coverings may occur in buildings at industrial parks. Some glass in most high-rise office buildings may be blown out; a few of these buildings may have minor to moderate damage and higher proportion of blown-out windows due to swaying. Considerable airborne debris will be generated and may cause damage, injury, and possible fatalities. Near total loss of power supply and telecommunications due to numerous downed power lines, poles, and cellular towers. Diminished availability of potable water supply is also likely. Significant to severe disruption to public transportation. Significant damage to banana and similar plants. Most small trees and some large trees will be broken, defoliated, or uprooted. Almost total damage to rice and other crops	Typhoons and stronger
	Extreme typhoon-force winds:Beaufort Force 12 ≥185 km/h ≥100 kn ≥51.3 m/s ≥115 mph	12 hours	Extreme threat to life and property Severe to catastrophic damage is expected to houses of poor or average construction, makeshift or old, dilapidated structures, and other structures made of light materials. Well-constructed houses may suffer substantial roof and wall failure or damage. Many industrial buildings will be destroyed, with only few receiving partial roof and wall damage. Most windows will be blown out in high-rise office buildings; moderate structural damage is possible due to swaying. Most, if not all, billboards and signs will be destroyed. Extensive damage will be caused by airborne debris. People, pets, and livestock exposed to the wind are at great risk of injury or death. Electricity, potable water supply, and telecommunications will be unavailable for prolonged periods due to significant disruption in infrastructure. Prolonged significant to severe disruption to public transportation. Vast majority of the trees will be broken, defoliated, or unrooted. Banana and similar plants will be extensively damaged. Only few trees, plants, and crops will survive.	Super typhoons

Issuance principles and practices

Whenever a tropical cyclone forms inside or enters the Philippine Area of Responsibility, the Philippine Atmospheric, Geophysical, and Astronomical Services Administration commences the release of Tropical Cyclone Bulletins to inform the general public of the cyclone's location, intensity, movement, circulation radius and its forecast track and intensity for at most 72 hours. The TCB also contains a plain-text discussion of the hazards threatening land and coastal waters and the PAGASA's track and intensity outlook for the cyclone.
PAGASA activates the five-tiered Tropical Cyclone Wind Signal system once it is determined that the tropical cyclone inside the PAR is going to directly affect the Philippines and its outermost cyclonic winds are 36 hours away or less from reaching the nearest Philippine landmass. Wind signals under the TCWS system are hoisted primarily at the city/municipal or province level; an exception is Metro Manila, which is collectively placed under a single wind signal level. All TCWS signal levels in effect in various localities affected or to be affected by tropical cyclone winds are enumerated in each TCB issuance, including the escalation, de-escalation or lifting of such signal levels. Wind signals are hoisted and updated usually in regular time intervals coinciding with the release of a TCB:

6-hourly TCB issuance: when TCWS signals levels have been raised as the tropical cyclone approaches the Philippine landmass.
3-hourly TCB issuance: when the tropical cyclone is about to make landfall within the next 24 hours; during land crossing and directly after land crossing when the tropical cyclone starts to move over water away from land; the tropical cyclone remains offshore but is significantly close to the landmass, warranting the activation of TCWS signals.

TCBs can also be released only twice a day when the tropical cyclone is too far away that it does not affect the Philippine landmass, in which case no TCWS signals are raised.
The TCWS system is a tiered system that allows for the escalation, de-escalation or lifting of wind signals in every TCB issuance depending on the tropical cyclone wind intensity, the extent of tropical cyclone winds and the forecast direction and speed of movement of the tropical cyclone at the time of TCB issuance. As a tropical cyclone approaches or moves over land, intensifies or becomes wider, a wind signal raised over a particular locality can be escalated to a higher wind signal level; multiple wind signals hoisted over various areas can also be escalated, and the extent or area where there are active wind signals can also be expanded. On the other hand, wind signals are de-escalated to lower wind signal levels, lifted or deactivated, and the area where wind signals are active becomes smaller when the tropical cyclone moves away from land, weakens or scales down in width. The TCWS system also allows for the skipping of wind signal levels, especially when there is a rapid change in the state of the tropical cyclone.
An important feature of the TCWS system is the lead time, which is the period within which a locality should expect the arrival of a range of tropical cyclone wind intensity, i.e. the number of hours from the first time a wind signal is hoisted until the expected range of tropical cyclone wind intensity starts impacting a particular locality. This makes the TCWS an early warning system, wherein the initial issuance of a specific signal level over a locality does not mean that the inclement weather conditions indicated for the given signal level are already prevailing. The lead time is used to raise awareness of the approximate remaining time for the public to prepare against impending tropical cyclone winds. Lead times in the TCWS system are valid only for the first issuance of a particular wind signal; higher wind signal levels correspond to higher wind speeds and shorter lead times.
For example, winds of 39–61 km/h are expected to occur within the next 36 hours when a specific locality is initially placed under TCWS #1 due to an approaching tropical cyclone; thus, that locality has at least 36 hours to prepare before such winds arrive or start to occur. When the wind signal in the same locality is escalated to #2, the public has at least 24 hours left to prepare or brace themselves before their locality is struck by winds of 62–88 km/h.
Contrary to common misconception and as implied by its name, the purpose of the TCWS system is to warn the public of the threat of tropical cyclone winds, including its associated hazards and/or impacts on land areas. As detailed in the table above, PAGASA devised the TCWS system such that each of the five warning signals stands for specific levels of severity of the impacts of tropical cyclone winds, especially on damages to infrastructure and agriculture due to high winds and the risk of injury or death due to building failure or airborne debris. The scope of the TCWS system does not include rainfall induced by tropical cyclones. PAGASA already has other warning systems for rainfall, such as Rainfall Advisories for light to moderate rainfall and the Heavy Rainfall Warning System for heavy and/or continuous rainfall during rain-intensive weather events, including tropical cyclones.
The TCWS system is often the basis for suspension of work, classes and transportation in the Philippines due to tropical cyclones. However, this is not explicitly stated since it is outside PAGASA's purview. The currently applied protocol by the country's Department of Education indicates that classes and work are automatically suspended in all public elementary and secondary schools located in localities where the TCWS system is in effect due to a tropical cyclone. However, current protocols implemented by the Commission on Higher Education stipulate that state universities and colleges are allowed to suspend classes and work due to tropical cyclones only in the following three cases: if the institution's locality has been placed under Wind Signal #3, if the local chief executive, i.e. municipal or city mayor, declares the suspension of work and classes in all levels, if the institution's head, i.e. president, headmaster or dean, declares the suspension of work and classes. On the other hand, the country's Coast Guard decrees that generally, all vessels are prohibited from venturing out to sea when the TCWS is in effect along its route and points of departure and destination, with strict exemptions applied only to few vessel types.