San Juan weather in December

Averages from 2021–2025 (155 days of record).

Average high: 83°F
Average low: 74°F
Rainy days: ~16 per month
Total precipitation: 2.7 in
Warmest recorded: 88°F
Coldest recorded: 66°F

Expect December days in San Juan to top out around 83°F and cool to about 74°F overnight, with roughly 16 days of measurable rain across the month. In recent years December has ranged from 66°F to 88°F.

Other months

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Current San Juan forecast → · Historical data by Open-Meteo (ERA5).