11/5 Ormoc flash flood

Last friday, November 5 is the 13th commemoration of the 1991 flash flood that hit Ormoc City, the city on western Leyte, Philippines. I hail from Ormoc, but I wasn't there by that time to witness it. I just relied on video footage months later. I tell you, I could not believe what I see. Just as everyone else, I kept asking why.
I was second year at City High when the DOST (Dept. of Science and Technology) held a symposium on it. The flash flood according to its findings was caused by the following: denuded forest (forest is less than 5% of the total land cover of the mountains surounding the city), heavy rain (brought by typhoon Uring), tornadoes (believe me tornado exists in this part of the country), and seiches (seasonal high tide or tidal wave, note: not a tsunami; the city proper is just at sea level).
These ingredients seem not to warrant a flash flood. But it happened. Why it killed an estimated 5,000 (as far as I remember) in less than an hour easily makes this disaster the most intense in terms of death that hit the country in recent times.