Climate of Puerto Rico

The climate of Puerto Rico in the Koppen climate classification is tropical rainforest. Temperatures are warm to hot year round, averaging near 85 °F (29 °C) in lower elevations and 70 °F (21 °C) in the mountains. Easterly trade winds pass across the island year round. Puerto Rico has a rainy season which stretches from April into November. The mountains of the Cordillera Central are the main cause of the variations in the temperature and rainfall that occur over very short distances. The mountains can also cause wide variation in local wind speed and direction due to their sheltering and channeling effects adding to the climatic variation. About a quarter of the annual rainfall for Puerto Rico, on average, occurs during tropical cyclones, which are more frequent during La Niña events.

Temperatures range from 70 to 90 °F (21 to 32 °C) in the lower elevations, while higher elevations in the central part of the island experience temperatures between 61 and 80 °F (16 and 27 °C) year round. The temperature in the south is a few degrees higher than the north. Between winter and summer, there is only a temperature swing of around 6 °F (3.3 °C). Coastal waters temperatures average between 77 °F in February to 87 °F in August. The highest temperature ever recorded was 103 °F (39 °C) at San Lorenzo, while the lowest temperature ever recorded was 38 °F (3 °C) at Aibonito.

Persistent 19-knot (35 km/h; 22 mph) trade winds move from east to west across the island year round. In lighter wind regimes, sea breeze and land breeze circulations dominate. Higher winds occur in the vicinity of tropical cyclones, which pass by every five years.

There is a pronounced rainy season from April to November. Due to the colony's topography, rainfall varies greatly across the island. Pico del Este averages 171.09 inches (4,346 mm) of rainfall yearly while Magueyes Island averages only 29.32 inches (745 mm) a year.

The Wet Season begins in May and lasts to late October. The weather is hot and humid with thunderstorms in the afternoon, especially in August and September. Trade winds bring cool summer breezes in the north and east of Puerto Rico, but due to the topography of the island, these winds do not reach the coast south and west, causing much higher temperatures than in the north. During humid summer days, the heat index can reach 115 °F (47 °C) and actual temperatures can reach 100 °F (38 °C). Sometimes the wind shifts from the south, causing an inverse, where the heat south of the island moves to the north, causing temperatures in the mid 90s (35 °C) in San Juan and low humidity. The month of June is usually the driest month of the summer. During June and July the precipitation is mostly caused by the effects of humidity and heat of the island. The peak of the hurricane season comes in September. Weather conditions can be very rainy as tropical lows pass near the island, with frequent strong thunderstorms. By early November the tropical cyclone season fades and the weather becomes drier and sunny generally.

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Wikipedia