Wait until summer to seal?
It would be best to wait for a couple of dry, sunny days before applying exterior sealant, but if you fear that rain will enter through the window edges it may be necessary to execute an emergency repair. If you have a 2-3 hour window of no rain in the forecast start the repair by removing only the sealant on the window edges that show the easiest routes into the house (lower horizontal edges?). The sealer will remove easier if you slice both edges with a razor knife. Coax the sealer off with a putty knife. Once removed apply (in order of best at sealing): 1) 100% silicone caulking, 2) window putty or glazing and 3) latex caulking. Use a caulk gun for all 3 suggestions. 100% silicone is hard to shape but seals the best. #2 and #3 are the easiest to work with; they seal sufficiently, but need at least 4-6 hours to become rain repellent (a hair dryer will shorten dry time).