Last updated: June 24, 2025
In San Juan, United States, the average temperature in December is a mild 18°C (64°F). However, temperatures can fluctuate significantly, with a minimum of 1°C (34°F) and a maximum reaching 34°C (94°F). Expect about 21 mm (0.8 in) of precipitation over approximately 3 days, accompanied by a relatively high average humidity of 86%. Enjoy the variety this month has to offer!
In December in San Juan, the average temperature is 18°C (64°F). The maximum can reach 34°C (94°F), while the minimum can drop to as low as 1°C (34°F). This range of temperatures makes San Juan a versatile destination for travelers, offering both warm and cool experiences to enjoy.
In San Juan in December, the precipitation amount is 21 mm (0.8 in) over a period of 3 days.
In San Juan in December humidity is 86%. With an average temperature of 18°C (64°F), this humidity feels like a warm embrace, making travel slightly uncomfortable as the air becomes thick and sticky, often leading to clammy skin and a constant need for hydration.
In San Juan in December, the maximum UV index is 6, which corresponds to a high Exposure Category. The time to burn is approximately 25 minutes. To find the hourly UV index in San Juan, you can refer to this Hourly UV Index in San Juan.
UV Risk Categories
Weather in San Juan varies notably across the year, with each month offering distinct climate conditions. This page compares December’s weather to other months in San Juan, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | 16°C (62°F) | 20 mm (0.8 inches) | 83% | high |
| February Weather | 18°C (65°F) | 21 mm (0.8 inches) | 79% | very high |
| March Weather | 22°C (72°F) | 31 mm (1.2 inches) | 76% | very high |
| April Weather | 25°C (78°F) | 31 mm (1.2 inches) | 77% | extreme |
| May Weather | 28°C (83°F) | 87 mm (3.4 inches) | 80% | extreme |
| June Weather | 30°C (86°F) | 81 mm (3.2 inches) | 73% | extreme |
| July Weather | 30°C (87°F) | 100 mm (3.9 inches) | 66% | extreme |
| August Weather | 31°C (88°F) | 22 mm (0.9 inches) | 65% | extreme |
| September Weather | 29°C (84°F) | 96 mm (3.8 inches) | 73% | extreme |
| October Weather | 25°C (77°F) | 51 mm (2.0 inches) | 76% | very high |
| November Weather | 20°C (69°F) | 30 mm (1.2 inches) | 80% | high |
| December Weather | 18°C (64°F) | 21 mm (0.8 inches) | 86% | high |