While the Philippines is no stranger to typhoons and tropical storms, the slow-moving nature of Koppu means heavy rain will fall for longer than usual, bringing greater risk of flooding and landslides.
It is the second strongest storm to hit the archipelago this year.
There are two typhoons in the west Pacific at the moment - Typhoon Champi sits just to the east of Koppu.
The complex interaction between these two typhoons and the warm air within these storms helps to build a ridge of high pressure over Taiwan this weekend. It is this ridge that effectively traps typhoon Koppu over the Philippines for a number of days rather than it being able to turn away from the Philippines and out of harm's way to the South China Sea.