The pilot was moving his float equipped airplane from his pier to the other side of the lake in order to dock his airplane at his friend’s pier temporarily. He decided to fly it to the other side of the lake instead of performing a water taxi. He departed into the wind. During climbout, he encountered heavy rain showers which obscured his forward visibility out the windshield. He executed a downwind landing to the lake by looking out the side window. He reported that during the landing, he could not slow the airplane down enough to avoid hitting a pier. The airplane sustained structural damage to the fuselage.