User:Chlod/Scripts/Deputy/testpages/TCWS
The Tropical Cyclone Wind Signals (TCWS, or simply storm signals or signals) are storm signals issued by the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) when a storm is inside or near the Philippine Area of Responsibility. TCWS signals are issued for specific localities depending on the expected strength of winds within a given amount of time (known as the lead time). The TCWS is a tiered system that has five levels, with higher numbers associated with higher wind speeds and shorter lead times.
| Signal No. | Issued for | Meaning |
|---|---|---|
| TCWS #1 | Tropical depressions and stronger |
winds of 39–61 km/h (24-38 mph) are prevailing or expected to occur within 36 hours |
| TCWS #2 | Tropical storms and stronger |
winds of 62–88 km/h (39–55 mph) are prevailing or expected to occur within 24 hours |
| TCWS #3 | Severe tropical storms and stronger |
winds of 89-117 km/h (55–73 mph) are prevailing or expected to occur within 18 hours |
| TCWS #4 | Typhoons and stronger |
winds of 118–184 km/h (73–114 mph) are prevailing or expected to occur within 12 hours |
| TCWS #5 | Super typhoons | winds greater than 185 km/h (115 mph) are prevailing or expected to occur within 12 hours |
Issuance
[edit]Tropical Cyclone Wind Signals are raised usually by province or city (with the exception of Metro Manila) by the PAGASA when a tropical cyclone is within the Philippine Area of Responsibility. On some occasions, signals may be raised for a specific municipality or city, depending on the storm. The TCWS is a tiered system goes from Signals No. 1 to 5, with higher signals meaning higher wind speeds and shorter lead times. The signal raised for a specific locality may change depending on the cyclone wind speed, intensity, extent of winds, direction, and movement speed.[1] TCWS signals are raised and lowered whenever Tropical Cyclone Bulletins are released by the PAGASA, which varies in 3-hour, 6-hour, and 12-hour intervals, depending on a storm's intensity and distance from the Philippines.[2]
The lead time determines the number of hours from the first time a signal is raised until an area is hit by the signal's expected wind strength. This means a storm signal may be hoisted in a locality hours before the impact of the winds are felt, in order to warn citizens of an impending storm.[1][3]
History
[edit]Public Storm Warning Signals
[edit]In the 1950's, the PAGASA (then the Philippine Weather Bureau) maintained a warning system which included 10 levels, from Public Storm Warning Signals (PSWS) #1 to #10. It was revised in the 1970s to include only three levels. A storm must have a maximum sustained wind speed of less than 63 kilometres per hour (39 mph; 34 kn) for PSWS #1 (equivalent to a tropical depression), 64 to 117 kilometres per hour (40 to 73 mph; 35 to 63 kn) for PSWS #2 (equivalent to a tropical storm) and at least 118 kilometres per hour (73 mph; 64 kn) for PSWS #3 (equivalent to a typhoon).[4]
| Signal No. | Meaning |
|---|---|
| PSWS #1 | winds less than 63 km/h (39 mph; 34 kn) |
| PSWS #2 | winds 64–117 km/h(40 to 73 mph; 35 to 63 kn) |
| PSWS #3 | winds greater than 118 km/h (73 mph; 64 kn) |
A fourth signal was added in 1997 to accommodate stronger typhoons. In addition to this, signals also included a lead time which determined when an area should expect the winds for a given signal. The PAGASA later expanded this to included details on a signal's impact and precautionary measures to be taken.[4]
| Signal No. | Meaning |
|---|---|
| PSWS #1 | winds 30 km/h (19 to 37 mph; 16 to 32 kn) expected in at least 36 hours |
| PSWS #2 | winds 60–100 km/h (37 to 62 mph; 32 to 54 kn) expected in at least 24 hours |
| PSWS #3 | winds 100–185 km/h (62 to 115 mph; 54 to 100 kn) expected in at least 18 hours |
| PSWS #4 | winds greater than 185 km/h (115 mph; 100 kn) expected in at least 12 hours |
Tropical Cyclone Warning System
[edit]Following the onslaught of Typhoon Haiyan in 2013, discussion on the revision of the PSWS started, as PSWS #4 was deemed inadequate for strong typhoons.[5][4] The Tropical Cyclone Warning Signal (TCWS) system was launched in May 2015 to replace the PSWS. Signals No. 1 to 4 followed the Western Pacific tropical cyclone basin's Regional Specialized Meteorological Center's scale, the scale used by the Japan Meteorological Agency. A fifth signal, TCWS #5, was introduced for super typhoons designated by the PAGASA. TCWS #5 carried the same lead time as TCWS #4: 12 hours.[4] The TCWS was then renamed to Tropical Cyclone Wind Signal in 2019 to give emphasis to winds rather than rains, flash floods, and landslides.[6]
| Signal No. | Equivalent category | Meaning |
|---|---|---|
| TCWS #1 | Tropical Depression | winds of 30–60 km/h (20-37 mph) are prevailing or expected to occur within 36 hours |
| TCWS #2 | Tropical Storm | winds of 61–120 km/h (38–73 mph) are prevailing or expected to occur within 24 hours |
| TCWS #3 | Severe Tropical Storm | winds of 121–170 km/h (74–105 mph) are prevailing or expected to occur within 18 hours |
| TCWS #4 | Typhoon | winds of 171–220 km/h (106–137 mph) are prevailing or expected to occur within 12 hours |
| TCWS #5 | Super typhoon | winds greater than 220 km/h (137 mph) are prevailing or expected to occur within 12 hours |
Shortly after the onslaught of Tropical Storm Megi, on March 23, 2022, the PAGASA revised the TCWS system again. The Modified Tropical Cyclone Warning System was implemented due to indistinguishable damages between areas under TCWS #4 and TCWS #5, and to refocus TCWS #2, which were issued for both tropical storms and severe tropical storms, despite the possible significant change in cyclone strength between the two.[5]
See also
[edit]References
[edit]- ^ a b "Tropical Cyclone Wind Signal". bagong.pagasa.dost.gov.ph. Retrieved 2022-06-30.
This article incorporates text from this source, which is in the public domain.
- ^ "Products and Services". www.pagasa.dost.gov.ph. Retrieved 2022-06-30.
- ^ PAGASA. "The Modified Philippine Public Storm Warning Signals". PAGASA Kidlat. Archived from the original on 2008-09-30. Retrieved 2008-09-30.
- ^ a b c d Esperanza O. Cayanan (July 20, 2015). "The Philippines modified its Tropical Cyclone Warning System" (PDF). World Meteorological Organization (WMO).
- ^ a b "DOST-PAGASA modifies Tropical Cyclone Wind Signal (TCWS) system". www.pagasa.dost.gov.ph. Retrieved 2022-06-30.
- ^ Arceo, Acor (2019-12-03). "Why is it now called tropical cyclone 'wind' – and not 'warning' – signals?". RAPPLER. Retrieved 2022-06-30.
- ^ PAGASA. "Philippine Tropical Cyclone Warning Signal". Archived from the original on 2022-06-30. Retrieved 2022-06-30.
Category:Tropical cyclone meteorology Category:Weather warnings and advisories