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
The first month of the winter, December, is also a moderately hot month in San Juan, Puerto Rico, with average temperature varying between 73.4°F (23°C) and 83.8°F (28.8°C).

Temperature

In December, the average high-temperature is relatively the same as in November - a still warm 83.8°F (28.8°C). In December, the average low-temperature is 73.4°F (23°C).

Heat index

The average heat index is appraised at a hot 91.6°F (33.1°C). Take special precautions - heat exhaustion and heat cramps are expected. Heatstroke may occur with lengthy activity.
Take into consideration that the heat index values are calculated for shade and light wind conditions. With the exposure to direct sunlight, the heat index may be increased by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'felt air temperature', 'apparent temperature', 'feels like', or 'real feel', is calculated by taking the relative humidity value for a specific location and factoring it into the air temperature reading. This effect is subjective, depending on the activity and individual's heat perception influenced by various reasons (pregnancy, differences in body mass, height, and shape, metabolic differences). Bear in mind that direct sunshine exposure increases weather impact, and may raise heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are particularly important for children. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.

Humidity

In San Juan, the average relative humidity in December is 74.7%.

Rainfall

In San Juan, in December, it is raining for 19.6 days, with typically 5.9" (151mm) of accumulated precipitation. Throughout the year, in San Juan, Puerto Rico, there are 198.5 rainfall days, and 70.6" (1794mm) of precipitation is accumulated.

Ocean temperature

In San Juan, Puerto Rico, the average water 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

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

Sunshine

In San Juan, Puerto Rico, the average sunshine in December is 7h.

UV index

January and December, with an average maximum UV index of 8, are months with the lowest UV index in San Juan. A UV Index of 8 to 10 symbolizes a very high health vulnerability from unprotected exposure to the Sun's UV rays for the ordinary person.
Note: The average daily UV index of 8 transform into the following instructions:
Take extra precautions. Protection against sun damage is required. 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 83.8°F (28.8°C), and the average low-temperature is 73.4°F (23°C). In December, the average heat index (a.k.a. 'feels like', 'apparent temperature'), that factores the actual air temperature with the relative humidity, is estimated at 91.6°F (33.1°C).

What is the average humidity in December in San Juan?

The average relative humidity in December in San Juan, Puerto Rico, is 74.7%.

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

In San Juan, in December, it is raining for 19.6 days, with typically 5.9" (151mm) of accumulated precipitation.

What is the water temperature in December in San Juan?

In December, the average ocean temperature in San Juan, Puerto Rico, 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?

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

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

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

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

In San Juan, Puerto Rico, the average sunshine in December is 7h.

When is the lowest UV index in San Juan?

January and December, with an average maximum UV index of 8, are months with the lowest UV index.

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

In December, the average daily maximum UV index in San Juan, Puerto Rico, is 8. A UV Index estimate of 8 to 10 represents a very high health vulnerability from the exposure to the Sun's UV rays.
Average temperature in December - San Juan, PR
  • Average high temperature in December: 83.9°F

Warmest months (with the highest average high temperature) are August and September (89.2°F).
The month with the lowest average high temperature is January (83.2°F).

  • Average low temperature in December: 73.4°F

The month with the highest average low temperature is August (78.2°F).
Coldest months (with the lowest average low temperature) are January and February (72°F).

Average humidity in December - San Juan, PR
  • Average humidity in December: 74.7%

The month with the highest relative humidity is October (76.9%).
The month with the lowest relative humidity is March (71%).

Average rainfall in December - San Juan, PR
  • Average rainfall in December: 5.9"

The wettest month (with the highest rainfall) is August (7.7").
The driest month (with the lowest rainfall) is March (3.1").

Average rainfall days in December - San Juan, PR
  • Average rainfall days in December: 19.6 days

Months with the highest number of rainy days are November and December (19.6 days).
The month with the lowest number of rainy days is March (12.2 days).

Average sea temperature in December - San Juan, PR
  • Average sea temperature in December: 81.8°F

The best month for swimming (with the highest average sea temperature) is September (84.9°F).
The coldest month (with the lowest average sea temperature) is February (78.9°F).

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: 7h

Months with most sunshine are March and July (Average sunshine: 9.1h).
The month with least sunshine is November (Average sunshine: 6.7h).

Average UV index in December - San Juan, PR
  • Average UV index in December: 8

Months with the highest UV index are March, April, May, June, July, August and September (UV index 12).
Months with the lowest UV index are January and December (UV index 8).