December weather forecast
San Juan, PR

December closes the year in San Juan with clear winter signals. Average high temperatures fall to a low of 80.8°F (27.1°C), constituting the perfect recipe for a comfortable holiday season. The sea temperature dips to 81.8°F (27.7°C), and the daylight hours decrease to 11 per day. Consistently, cloud coverage increases to 35%, the highest for the year, offering a cosy shield from the sun. The city's serene ambiance during this month makes it an enticing destination for holiday travellers looking for a temperate getaway.

Temperature

During December, San Juan records an average high-temperature of a still moderately hot 80.8°F (27.1°C), marking a slight divergence from November's 83.1°F (28.4°C). San Juan records a consistent average nighttime temperature of 75.9°F (24.4°C) in December, slightly lower than the daytime high.

Heat index

For December, the heat index is calculated to be a hot 86°F (30°C). Unrelenting activity during exposure could cause fatigue and potentially lead to heat cramps.
It is worth noting that heat index values are gauged for conditions in the shade and light breezes. Direct sunlight might lead to a heat index increase by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'apparent temperature' or 'felt air temperature', combines air temperature and relative humidity to represent a human perceived temperature equivalent. An individual's temperature experience can be influenced by extra factors, including metabolic differences, activity levels, and clothing. It is essential to realize that direct sunlight can escalate the perceived temperature, increasing the heat index by 15 Fahrenheit (8 Celsius) degrees. Heat index values hold great significance to children. Children usually face more risks than adults as their ability to sweat is less. Additionally, their larger skin surface in relation to their petite bodies and higher heat output due to their activities increases their vulnerability.

Humidity

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

Rainfall

In San Juan, Puerto Rico, during December, the rain falls for 14.5 days and regularly aggregates up to 0.98" (25mm) of precipitation. In San Juan, Puerto Rico, during the entire year, the rain falls for 159.9 days and collects up to 12.01" (305mm) of precipitation.

Ocean temperature

In San Juan, in December, the average water temperature is 81.9°F (27.7°C).
Note: For swimming, diving, and enjoying other water activities, the range of 77°F (25°C) to 84.2°F (29°C) in water temperature is considered ideal, offering pleasure for extended periods without discomfort.

Daylight

The month with the shortest days is December, with an average of 11h and 0min of daylight.
On the first day of December, sunrise is at 6:40 am and sunset at 5:46 pm. On the last day of the month, sunrise is at 6:56 am and sunset at 5:59 pm AST.

Sunshine

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

UV index

The months with the lowest UV index in San Juan 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 hazard from exposure to the Sun's UV radiation for the ordinary person.
Note: A maximum high UV index of 6 in December translates into the following recommendations:
Guard against overexposure. Protection from sun-induced harm is essential. Seek shade and limit direct Sun exposure between 10 a.m. and 4 p.m., when UV radiation is at its peak, but be aware that not all shade structures provide complete sun protection. Safeguard your eyes, ears, and face from sun rays with the aid of a wide-brim hat. Be vigilant! The Sun's UV rays get a boost from sand and water reflections.