1999 Honda Accord Wiper blades

Hello. When it is raining and my wiper blades are turned on, the wiper blades swing all the way across the windshield and slam into the side of the windshield. When the wiper blades go back down to their normal position, they slam all the way down onto the plastic part below the windshield. I have also noticed that making a right turn as the windshield wipers are on also helps the wiper blades swing all the way accross the windshield. I have tried to tighten the nuts at the end of the wiper blades but they are tight. What could be the problem? Thanks.