Inform ATC of your current conditions: "Vienna Information, OE-LAB, two thousand feet, wind 220 at 15 knots, visibility four kilometers, rain. Unable to maintain current routing due to weather."
Request a clearance to better conditions: "Request descent to one thousand five hundred feet and heading one-eight-zero to exit precipitation."
Request a routing change if necessary: "Request clearance for right turn thirty degrees to avoid weather ahead."