Typhoons form when warm waters causes the air above it to swirl, forming the destructive weather systems as we know it. When there's enough stretch of warm water to gather strength before hitting land, it becomes a Super Typhoon.
Super Typhoons are rare, but are always remembered for their raw power. Weather bureau PAGASA defines a super typhoon as one with at least 220 kph of maximum sustained winds near the center.
Rolly (international name: Goni) is expected to peak at super typhoon strength Saturday before weakening back to a typhoon when it hits land later Sunday. Authorities have told millions on the storm's path to brace for impact, with Signal no. 4 (the second highest) possible. Winds can blow off roofs and topple billboards, PAGASA said.
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Yolanda changed the way we see Super Typhoons
When Yolanda slammed into the Central Philippines in 2013, it was the strongest storm ever recorded. Known internationally as Haiyan, it whipped storm surges and wiped out entire communities leaving some 6,000 people dead or missing.
It also changed the Philippines' definition of super typhoons -- to maximum sustained winds of 220 kph from 200 kph. Storm signal warnings were also changed to a scale of 1 to 5 from just 1 to 4.
The weather bureau also laymanized its forecasts, making them more practical and visual. When Signal no. 2 is raised, GI sheet roofs could be pelled off and wooden posts could get tilted, PAGASA said.
Ondoy showed the threat of rains
In 2009, Ondoy (Ketsana) spawned epic flooding in Metro Manila, inundating entire villages. Not even a typhoon, Ondoy showed how typhoons can stir monsoon rains. There was no Signal no. 4, but the damage to the capital was unprecedented.
Never before has a typhoon submerged so many cars that people were made aware that their insurance coverage may or may not include so-called Acts of God like Ondoy.
Ondoy prompted a water-level warning system on the Marikina River. Now, residents keep a close watch on it, even if there's no typhoon, to gauge whether or not they should evacuate.
Since Ondoy, Malacanang also started investing in Doppler Radars to provide rainfall forecasts, even when there's no typhoon.