As an archipelago in Western North Pacific, the Philippines is exposed to tropical cyclones of varying intensity and impacts at an average frequency of 20 tropical cyclones a year. To mitigate or reduce the damages caused by this disastrous phenomenon, the Philippine Weather Bureau, the national meteorological-hydrological service now known as Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), established the Tropical Cyclone Warning System (TCWS).
n 1950’s, the TCWS involved 10 warning levels: Public Storm Warning Signal (PSWS)# 1 to PSWS #10. Basically, the warning system was designed for mariners at sea. Visual storm warning signs in the form of cones and cylinders are hoisted prominently on masts in ports. Night signals are in the form of red and white lamps. In 1970’s, the number of warning levels was reduced from 10 to three (3) using the three WMO tropical cyclone category as basis. The warning levels then are: PSWS #1: max winds <63 kph for Tropical Depression; PSWS #2: max winds 64 -117 kph for Tropical Storm; and PSWS #3: max winds >118 kph for Typhoon. In 1997, there was motion to upgrade the warning levels to four (4) for the reason that the number of warning signals is inadequate for strong typhoons. Hence, the signals used was PSWS #1 to PSWS # 4 with the addition of time element: PSWS # 1: Winds 30-60 kph -expected in at least 36 hrs; PSWS # 2: Winds >60-100 kph -expected in at least 24 hrs; PSWS # 3: Winds >100-185 kph -expected in at least 18 hrs; and PSWS # 4: Winds >185 kph -expected in at least 12 hrs. Some changes such as addition of meteorological conditions, impacts of the winds and precautionary measures were made later in 2010.