Complex sentence: The wettest months of the year are April and May in western areas, but closer to the coast, September becomes the year's wettest month on average, for example at Corpus Christi, South Padre Island and Brownsville.
Split into simpler sentences: The wettest months of the year are April and May in western areas, but approaching the Gulf Coast, September becomes the year's wettest month on average. The resulting September monthly rainfall maximum prevails, for example, at Corpus Christi, South Padre Island and Brownsville.