San Juan
Puerto Rico, USA
Long-term weather forecast
Long-term weather forecast

December weather forecast and climate
San Juan, PR

An old fort building and a view of the stunning San Juan city, Puerto Rico, with a clear view of the calm waterfront
An old fort building and a view of the stunning San Juan city, Puerto Rico, with a clear view of the calm waterfront
December, the first month of the winter, in San Juan, is also a moderately hot month, with average temperature varying between 75.9°F (24.4°C) and 80.8°F (27.1°C).

Temperature

In December, the average high-temperature is practically the same as in November - a still warm 80.8°F (27.1°C). The average low-temperature, in San Juan, is 75.9°F (24.4°C).

Heat index

In December, the average heat index is calculated to 85.5°F (29.7°C). Exhaustion is likely with prolonged exposure and activity. Sustaining activity may result in heat cramps.
Note that heat index values are valued for light wind and location in the shade. Exposure to direct sunshine can increase heat index values by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'felt air temperature', 'real feel', 'apparent temperature', or 'feels like', is what the temperature feels like to the human body when the air temperature is combined with the relative humidity. Additional factors like metabolic differences, differences in body mass, height, and shape, pregnancy, and activity influence one's weather impression. Be aware that direct exposure to sunlight increases heat impact, and may raise the heat index additionally, by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are particularly important for children. Children are often less aware of the need to rest and re-hydrate. Thirst is a late sign of dehydration - it is vital to remain hydrated, particularly during prolonged physical activities.

Humidity

In San Juan, the average relative humidity is 77%.

Rainfall

In San Juan, in December, it is raining for 14.5 days, with typically 0.98" (25mm) of accumulated precipitation. In San Juan, during the entire year, the rain falls for 159.9 days and collects up to 12.01" (305mm) of precipitation.

Ocean temperature

In December, the average ocean temperature is 81.9°F (27.7°C).
Note: For any water activity, surface water temperatures between 77°F (25°C) and 84.2°F (29°C) are considered as excellent and extremely pleasant for lengthened periods.

Daylight

With an average of 11h of daylight, December has the shortest days of the year in San Juan.

Sunshine

December has the least sunshine of the year, with an average of 6.6h of sunshine.

UV index

Months with the lowest UV index are January through March and December, with an average maximum UV index of 6. A UV Index reading of 6 to 7 represents a high health vulnerability from the exposure to the Sun's UV radiation for the ordinary person.
Note: In December, the average maximum UV index of 6 translate into the following recommendations:
Take precautions against overexposure. Protection against sun damage is needed. The Sun's UV radiation is most powerful between 10 a.m. and 4 p.m. To the extent possible, limit exposure to the direct sun during these hours. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. Beware! The reflection of water and sand dramatically increases exposure to the UV rays.

What is the temperature in December in San Juan?

In San Juan, Puerto Rico, in December, the average high-temperature is 80.8°F (27.1°C), and the average low-temperature is 75.9°F (24.4°C). The average heat index (a.k.a. 'apparent temperature', 'real feel'), that combines both air temperature and relative humidity, in December is appraised at 85.5°F (29.7°C).

What is the average humidity in December in San Juan?

The average relative humidity in December in San Juan is 77%.

How many days does it rain in December in San Juan?

In San Juan, in December, it is raining for 14.5 days, with typically 0.98" (25mm) of accumulated precipitation.

How warm is the water in December in San Juan?

In San Juan, the average seawater temperature in December is 81.9°F (27.7°C). For any water activity, surface water temperatures between 77°F (25°C) and 84.2°F (29°C) are considered as excellent and extremely pleasant for lengthened periods.

What is the month with the shortest days in San Juan?

December has the shortest days of the year in San Juan, with an average of 11h of daylight.

How many hours of daylight does San Juan have in December?

In San Juan, the average length of the day in December is 11h.

What is the month with the least sunshine in San Juan?

December has the least sunshine of the year in San Juan, with an average of 6.6h of sunshine.

How long on average sun shines in December in San Juan?

In December, the average sunshine in San Juan, Puerto Rico, is 6.6h.

What is the month with the lowest UV index in San Juan?

January through March and December, with an average maximum UV index of 6, are months with the lowest UV index.

What is the UV index reading in December in San Juan?

The average daily maximum UV index in December in San Juan is 6. A UV Index value of 6 to 7 symbolizes a high hazard to health from the exposure to the Sun's UV rays.
Average temperature in December - San Juan, PR
  • Average high temperature in December: 27.1°C

The warmest month (with the highest average high temperature) is August (29.5°C).
Months with the lowest average high temperature are January and March (26.6°C).

  • Average low temperature in December: 24.4°C

Months with the highest average low temperature are August, September and October (26.2°C).
The coldest month (with the lowest average low temperature) is March (23.3°C).

Average humidity in December - San Juan, PR
  • Average humidity in December: 77%

Months with the highest relative humidity are May, June and July (79%).
Months with the lowest relative humidity are February and March (76%).

Average rainfall in December - San Juan, PR
  • Average rainfall in December: 25mm

The wettest month (with the highest rainfall) is November (40mm).
The driest month (with the lowest rainfall) is April (14mm).

Average rainfall days in December - San Juan, PR
  • Average rainfall days in December: 14.5 days

The month with the highest number of rainy days is November (16.1 days).
The month with the lowest number of rainy days is June (10.3 days).

Average sea temperature in December - San Juan, PR
  • Average sea temperature in December: 27.7°C

The best month for swimming (with the highest average sea temperature) is September (29.4°C).
Coldest months (with the lowest average sea temperature) are February and March (26.1°C).

Average daylight in December / Average sunshine in December - San Juan, PR
  • Average daylight in December: 11h

The month with the longest days is June (Average daylight: 13.2h).
The month with shortest days is December (Average daylight: 11h).

  • Average sunshine in December: 6.6h

The month with most sunshine is June (Average sunshine: 10.9h).
The month with least sunshine is December (Average sunshine: 6.6h).

Average UV index in December - San Juan, PR
  • Average UV index in December: 6

Months with the highest UV index are April, May, June, July, August, September, October and November (UV index 7).
Months with the lowest UV index are January, February, March and December (UV index 6).