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My fiance is from Cebu and we even talked about their incidence there and it is very uncommon. Of course you have a lot of convective activity that is associated with the ITCZ and Monsoonal activity but in certain instances these conditions are enhanced by localized upper air disturbances that allow for tornadic weather.

Typically these conditions are offset by terrain and other geographical reasons and they cannot form into tornadoes. Maybe the mass of your storms there do not permit the spin necessary for formation or the clouds are being sheared off for some reason. There are so many factors to consider.

Tornadoes can hit anywhere, I live in the UK and we get tornadoes here too (average 33 a year). The occurence of tornadoes is likely to escalate as the earth warms up. Tornadoes are caused by warm air clashing with colder air, this causes the warmer air to rise and create a very large thunder mass called a super cell. If there are down drafts and up drafts happening they usually start up horizontally, but if one is stronger it pulls the rotating winds into a vertical position whichcause area of the storm to rotate and that "gives birth" to tornadoes.

I believe the tornado was associated with a tropical low pressure system. These can and occasionally do produce tornadoes due to the very good wind shears associated with them. It is not normal, but at the same time it is not an unusual event.