Actually, the date of April 15th is considered the end of high season & that's why the lower rates kick in. Nothing to do w/ rain. However, it is tied to the weather improving in the spring in many areas of North America. People are more likely to travel to warm climates when it's cold where they live, not so inclined when it's warming up at home. Again, rainy season means hurricane season & that officially starts June 1. That doesn't mean it won't rain before then, it just isn't the official season for tropical weather that creates more rain, tropical storms, & hurricanes.