Puerto Rico has a mild Tropical Marine climate year round. Temperatures average 80 °F (26.7 °C) in the lower elevations and 70 °F (21.1 °C) in the mountains. Temperatures range from about 70 to 90 °F (21.1 to 32.2 °C) throughout the year although slightly cooler in the central mountain range. During the summer months the heat index can reach over 100 °F (37.8 °C) with high humidity, totally bearable if you are at the beach enjoying the sun and cool ocean breezes.
The rainy season runs from April to November with a Hurricane season similar to the rest of the Caribbean and the North Atlantic Ocean. Depending on where you are on the island, you may experience some periods of daily rain. This is particularly true in the western region but rest assured the sun will come out quickly drying things up. The southern region of Puerto Rico tends to be warmer and dryer than the north. Bring cool tropical clothing with a light jacket or sweater. Many office buildings and indoor shopping malls have excellent air conditioning so if you tend to be susceptible to cold having a jacket or sweater will keep you comfortable.