September in Puerto Viejo is the warmest month of the year. In September, the weather in Puerto Viejo is typically hot. Average daily high temperature in September is about 28 degrees above zero. On average, Puerto Viejo has 29 rainy and 1 partly cloudy day in September. The rains are usually heavy. September as well as April, May, June, and July is considered the most uncomfortable time to visit Puerto Viejo.