Advisory: PAGASA redefines Super typhoon, modifies wind signals

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Advisory: PAGASA redefines Super typhoon, modifies wind signals

Almost seven years after Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) added the Super typhoon category, it is now redefining its classification to conform with regionally accepted standards and best practices of other meteorological centers within the Northwest Pacific region.

In a press conference last March 23, the Philippines’ weather bureau announced that it will be implementing changes with the Tropical cyclone warning system (TCWS), including the threshold intensities for tropical cyclone (TC) categories, wind signals, and the TC forecast chart. 

Originally having a threshold intensity for maximum sustained winds of 220 km/h, a tropical cyclone will now be classified a Super typhoon once it reaches 185 km/h maximum sustained winds. The maximum intensity for the Typhoon category was also adjusted accordingly.

With this modification, PAGASA’s classification of a Super typhoon will be in consensus with other TC warning centers, such as Hong Kong Observatory (HKO), Macau Meteorological and Geophysical Bureau (MMGB), China Meteorological Administration (CMA), and Joint Typhoon Warning Center (JTWC). This naming convention will reduce the confusion among relevant stakeholders.

Upon implementation of the modified TC category and TCWS, TCs will be classified at a higher category than would be expected using the old classification scheme. A higher number of Super typhoons as well as higher warning signal number can be expected as the minimum intensity was reduced. This does not necessarily mean that TCs will grow stronger this year or in the coming years than the previous years’ (although that is a possibility because of climate change), but the expected increase in the number of higher category TCs and higher warning signal number is largely due to the adjusted intensity threshold.

The Modified Tropical Cyclone Wind Signal and updated Forecast Chart

Aside from the adjustment of the definition of a Super typhoon, PAGASA also announced the Modified Tropical Cyclone Wind Signal system. Under the new system, wind threat associated with each warning signal was modified to match the minimum intensities of each TC category. The wide range of wind speeds for signal no. 2 was reduced to take into account the increased severity of TC winds when upgrading from TS to STS. 

While the lead time remains the same, the description of potential impacts was further simplified. According to PAGASA, as it works towards impact-based forecasting, the potential impacts associated with each warning signal will be made more specific.

The forecast chart for the next Tropical cyclone advisory will also be updated to include the following features: 

  • Addition of 12-hr, 36-hr and 60-hr forecast positions and intensities for the first three-day segment of track and intensity forecast
  • Addition of TC wind area depicting the wind intensity over the region covered by the TC
    • Areas experiencing at least strong winds or signal nos. 1 or 2 will be colored in yellow-orange
    • Areas experiencing more destructive winds or signal no. 3 or higher will be colored in maroon
  • Use of new icons for each TC category
  • Resized probability cone, which represents the probable track of the center of the TC
    • The old format uses a 100km-radius coverage from 24-hr forecast position and 500km-radius coverage from 120-hr forecast position
    • For the new format, the probability cone coverage will be updated annually based on PAGASA forecast track performance in the past 5 years
  • Adjustment of the northern boundary of the TC forecast area from 25°N to 27°N

Please refer to the DOST-PAGASA Press Statement: “DOST-PAGASA Modifies Tropical Cyclone Wind Signal (TCWS) System” released on March 23 for more information. PAGASA also released videos on the Modified TCWS System on March 23 and an Orientation on the Tropical Cyclone Module for Senior High on March 24.