A brief history of cyclone warnings in the PHL

Supertyphoon Lawin's approach toward Luzon on Wednesday, October 19, marks the first time in history that Philippine state weather forecasters have used Tropical Cyclone Warning Signal No. 5.

The warning category, the highest in a five-level system unveiled by PAGASA in May 2015, was established in anticipation of "supertyphoons" the likes of Yolanda, which devastated the country just the year before.

Contrary to popular belief, cyclone warnings don't reflect the current weather in an area. Rather, they serve to warn the public of future wind conditions.

Under PAGASA's current warning system, the higher the signal, the stronger the wind and the shorter the lead time before the wind is felt. Generally, higher warning levels are also associated with stronger typhoons.

But things weren't always this way.

In contrast, until the 1990's, PAGASA used a much simpler 3-tier warning system that featured a fixed lead time of 16 to 18 hours:

The system was notable in its simplicity, with disaster historian Greg Bankoff remarking that it made a useful distinction between tropical depressions—which are welcomed by farmers for the rain they bring without life-threatening winds—and destructive typhoons.

"No such fine distinctions were made in the past. Known respectively by Filipino and Spaniard alike in the (Philippine) Islands as baguios, by the Portuguese in India and China as tifones, and as huracanes in Spain, there are a surprising number of historical sources on typhoons testifying to their importance whether or not their effect has been generally recognized in conventional history," Bankoff wrote.

PAGASA's system was later expanded to include a fourth warning level, which was first used on October 27, 1991, when Typhoon Trining hit Luzon:

It would be over two decades before authorities thought to revise the system yet again, in the wake of the unprecedented effects of Supertyphoon Yolanda.

To date, Yolanda is the strongest cyclone to make landfall in recorded history: travelling at an average speed of 40 kph, it struck the island of Eastern Samar with a peak strength of 314 kph. 

In response, almost a year to the day after Yolanda's landfall, PAGASA issued Memorandum Circular No. 3, expanding the agency's warning system and adding a "supertyphoon" category for cyclones with winds in excess of 220 kph.

The expanded system takes into account the growing number of very strong typhoons on record, but provides a shorter lead time ahead of the very strong winds usually found near the cyclone's eye.

A shorter lead time enables more accurate forecasts, but comes at a price: it leaves less time for the public to prepare for disaster. — GMA News 

TJ Dimacali spent three months in Singapore on the Temasek Foundation International-Nanyang Technological University Asia Journalism Fellowship in 2016. His focus was weather reporting practices.