In meteorology, the life cycle of a tropical cyclone starts with cloud clusters that develop into a low pressure area (LPA). Once this LPA intensifies, it becomes a tropical cyclone, the general term for “bagyo.” This tropical cyclone is then classified based on its wind speeds.
Through the years, the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) has used three official tropical cyclone categories: Tropical Depression, Tropical Storm and Typhoon.
Yolanda, with the international name Haiyan, which made its landfall in the country last November 2013, is remembered as one of the strongest typhoons in recent years. Largely affected was the Visayas area, where storm surges caused massive destruction to lives and properties.
Days before the first anniversary of Yolanda, the Typhoon Committee of PAGASA decided to revise the classification of tropical cyclones, adding the category “Super Typhoon” on its list. However, this memo said that the revision will be applied in 2015.
In May 2015, by virtue of Memorandum Circular No.3, PAGASA officially declared that Super Typhoon is now part of the tropical cyclone classification.
The new tropical cyclone classifications are as follows:
Tropical Depression (TD) has maximum sustained winds of up to 61 kilometers per hour, equivalent to 33 nautical miles per hour or more.
Tropical Storm (TS) packs 62 to 117 kilometers per hour. Meanwhile, a Severe Tropical Storm will only be applicable for the International Warning for Shipping, and will not be used for general public dissemination unlike the other categories.
Typhoon (TY) is used in identifying a tropical cyclone with wind speeds 118 to 220 kilometers per hour or 64 to 120 knots.
Super Typhoon (STY) has maximum sustained winds of more than 220 kilometers per hour. STY is as powerful as 120 nautical miles per hour or more.
Since there are changes in cyclone categories, the public storm warning signals (PSWS) were revised as well. According to PAGASA, the country has experienced a number of destructive tropical cyclones in the past ten years. These cyclones were mostly in Typhoon category with maximum sustained winds of more than 220 kilometers per hour. During the passage of Yolanda, the usual four-level warning system of the PSWS was found inadequate.
In line with this, Signal Number 5 now becomes part of PAGASA’s warning.
Once PSWS #5 is hoisted, residents must prepare for winds of more than 220 kilometers per hour in at least 12 hours. This can cause very heavy to widespread damage to the affected areas.
PAGASA explained that the revision aims to emphasize the intensity of a tropical cyclone and the threat of its impacts. Using the term “Super Typhoon” and “Signal Number 5” will also escalate the sense of urgency and community response in times of an approaching storm.