Sendong was a 'weak' storm ranked among most destructive in PHL history

Tropical Storm Sendong was a bizarre weather creature —  a "weak" storm by the standards of PAGASA yet it claimed more lives than any typhoon in more than a decade. Its destructiveness came from the rare and "very extreme" amount of rainfall dumped on northern Mindanao on Dec. 16. According to a new analysis of the storm by the scientific institution Manila Observatory, the 180 millimeters (mm) of rain that fell in Cagayan de Oro on that day far exceeded the previous record of 142mm in 1999. Rainfall has been measured in the Lumbia weather station in Cagayan de Oro since 1977. The same study by the Manila Observatory cited historical evidence that storms rarely make landfall in Mindanao. That fact has been used to explain why local officials and the public didn't show much of a response to warnings about Sendong's pending arrival. The Manila Observatory noted that in the last 15 years, only six tropical cyclones crossed Mindanao, and only one in 10 years in December. None of the previous Mindanao storms had this kind of impact. The Manila Observatory noted that Sendong ranked among the most destructive tropical cyclones in Philippine recorded history, including Uring (1991, Ormoc), Pepeng (2009, Northern Luzon), Juaning (2011, Bicol) and Ondoy (2009, Metro Manila). Yet all of them were classified as "weak", suggesting that PAGASA's current storm warning system, which takes into account only a storm's wind speed, is inadequate for indicating the potential danger of a coming storm. The rainfall-tracking Doppler radar systems that PAGASA recently acquired were supposed to remedy this deficiency, but weather forecasters pointed out after Sendong that only one was placed in Mindanao, where its effectiveness could be hampered by mountain ranges. But there are other ways of predicting rainfall. Just before Sendong made landfall in Mindanao, the United States’ National Aeronautics and Space Administration (NASA) had its Tropical Rainfall Measuring Mission (TRMM) satellite pass over the storm for a detailed scan. The resulting rainfall analysis showed that “Washi (Sendong) was much better organized with very heavy rainfall of over 50mm/hr (~2 inches) revealed by TRMM PR within bands spiraling into the center of the storm."   NASA forecast severe flood potential over many cities and towns in Mindanao. Sendong became a perfect storm of extreme rainfall pouring on areas of high vulnerability. The enormous volume of water interacted with denuded watersheds with piles of cut logs draining into narrow and densely populated flood-prone coastal lowlands. Residents still reeling from the effects of the storm cannot even take comfort in the notion that storms of this magnitude will continue to be rare. As the Manila Observatory concludes, "The scientific consensus is that extreme weather events are going to be more likely and frequent with climate change." — Howie Severino/VS, GMA News