Ford escort serpentine belt keeps coming off.when it rains?

I have a 98 escort zx2 every time it rains my serpentine belt comes off. I don't think its the tensioner because its so hard to pull when i put it back on. I've replaced the belt 3 times now due to it sheredding. Any other ideas? This is getting really annoying and getting another car isn't an option right now

Hi so three things get changed when the serpentine belt is changed the belt it's tensioner and the water pump why well the pulleys become worn and need to be replaced.

If the belt is shredding, think what is causing that. You pull it out and say to yourself, "its shredding". What causes shredding is too much tension on the belt like one of the pulleys is frozen up. Take the belt off and go through each pulley and make sure they are free. The rain is just the opportunity the belt needs to go off. Its not the cause.