The weather bureau has added an additional public storm warning signal—signal No. 5—to better reflect the potential dangers of supertyphoons like “Yolanda.

Vicente Malano, administrator of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) said the recent frequency of very strong typhoons has made the old four-level warning system “inadequate.”

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Malano signed the memorandum circular adopting the supertyphoon category signal on May 18 “to give emphasis” to the more dangerous and possibly devastating effects of supertyphoons or storms with winds above 220 kph.

Under the previous Pagasa warning system, the highest alert was signal #4, which indicated storms with wind velocities greater than 185 kph.

The memorandum noted that “for the past ten years, the Philippines has experienced a number of extremely damaging tropical cyclones, particularly typhoons with maximum sustained winds of more than 220 kph.”

“Because of this, the supertyphoon category. . .was adopted by Pagasa. These very strong typhoons, i.e., Yolanda, caused intensive and devastating damage which according to stakeholders made the four-level warning system inadequate,” it added.

The corresponding impact of winds was based on the typhoon damage scale proposed in a study conducted by former Pagasa administrator Leoncio Amadore.

According to Pagasa weather division chief Esperanza Cayanan, signal No. 5 warns not only of extremely strong winds but also of the possibility of big waves (more than 14 meters at open sea) and storm surges of more than three meters in affected coastal areas.

Signal No. 5 urges residents to beware of widespread damage to structures, particularly old and dilapidated homes and buildings. Most tall trees may be broken, uprooted or defoliated.

The modified public storm warning system is now as follows:

Signal No. 1 (Lead time 36 hours)—30-60 kph maximum sustained winds; expected impact of the wind: no damage to very light damage

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Signal No. 2 (Lead time 24 hours)—61-120 kph maximum sustained winds; light to moderate damage expected.

Signal No. 3 (Lead time 18 hours)—121-170 kph maximum sustained winds; moderate to heavy damage expected.

Signal No. 4 (Lead time 12 hours)—171-220 kph maximum sustained winds; heavy to very heavy damage expected.

Signal No. 5 (Lead time 12 hours)—more than 220 kph maximum sustained winds; very heavy to widespread damage expected.

The warning system was last revised in 2010.

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