2000 Chrysler Grand Voyager serpentine belt slips when wet

serpintine belt slipping off when it rains hard or belt get extra wet

This is a known problem for that model. I would suspect a bad belt tensioner. Additionally, the pulleys may not be aligned correctly.

How old is the belt? They stretch over time, and this one might need replacement if it is old.

Most parts stores sell a serpentine belt anti-slip shield for the Chrysler vans.