September weather forecast
San Juan, PR

An old fort building and a view of the stunning San Juan city, Puerto Rico
An old fort building and a view of the stunning San Juan city, Puerto Rico

Weather in September

September, the first month of the autumn in San Juan, is still a warm month, with an average temperature varying between 84.9°F (29.4°C) and 79.2°F (26.2°C).

Temperature

In San Juan, the average high-temperature in September is practically the same as in August - a still warm 84.9°F (29.4°C). In September, the average low-temperature is 79.2°F (26.2°C).

Heat index

In September, the average heat index is computed to be a sweltering 95°F (35°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 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 'real feel', 'felt air temperature', 'apparent temperature', or 'feels like', is an index that combines air temperature and relative humidity to determine the human-perceived temperature equivalent. This effect is individual, with diverse people perceiving weather differently for numerous reasons (pregnancy, metabolic differences, differences in body mass, height, and shape), and activity. Be aware that direct exposure to sunlight increases heat impact and may raise the heat index 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.
The human body cools itself through perspiration, as excessive warmth is removed from the body through sweat evaporation. With a lot of moisture in the air, the evaporation process is not as effective, and the body does not cool down as efficiently, creating a perception of overheating. When heat gain surpasses the level the body can shed, body temperature begins to increase, and consequently, overheating and dehydration can occur, with varying severity.

Humidity

In September, the average relative humidity is 78%.

Rainfall

In San Juan, during September, the rain falls for 11.7 days and regularly aggregates up to 1.18" (30mm) of precipitation. Throughout the year, in San Juan, Puerto Rico, there are 159.9 rainfall days, and 12.01" (305mm) of precipitation is accumulated.

Ocean temperature

September is the month with the warmest seawater, with an average ocean temperature of 84.9°F (29.4°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

In September, the average length of the day in San Juan is 12h and 14min.
On the first day of September in San Juan, sunrise is at 6:09 am and sunset at 6:39 pm. On the last day of the month, sunrise is at 6:14 am and sunset at 6:14 pm AST.

Sunshine

The average sunshine in September is 9.4h.

UV index

The months with the highest UV index are April through November, with an average maximum UV index of 7. A UV Index value of 6 to 7 symbolizes a high health hazard from exposure to the Sun's UV radiation for the average person.
Note: The daily maximum UV index of 7 in September interpret into the following advice:
Take precautions and adopt sun safety practices. Protection against sunburn is obliged. Seek shade and minimize exposure to direct Sun in a period between 10 a.m. and 4 p.m. when UV radiation is most intense; keep in mind that shade structures like parasols or canopies do not provide perfect sun protection. 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 strength of the UV rays is significantly increased by the reflection of the water and sand.
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FAQ

What is the temperature in September in San Juan?

In September, in San Juan, the average high-temperature is 84.9°F (29.4°C), and the average low-temperature is 79.2°F (26.2°C). in September, the average heat index (a.k.a. 'felt air temperature', 'real feel'), which combines air temperature and relative humidity, is computed to be 95°F (35°C).

What is the average humidity in September in San Juan?

In San Juan, the average relative humidity in September is 78%.

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

In San Juan, in September, it is raining for 11.7 days, with typically 1.18" (30mm) of accumulated precipitation.

What is the month with the warmest ocean in San Juan?

With an average ocean temperature of 84.9°F (29.4°C), September is the month with the warmest seawater in San Juan, Puerto Rico.

What is the water temperature in September in San Juan?

In San Juan, in September, the average water temperature is 84.9°F (29.4°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 average length of the day in September in San Juan?

In San Juan, the average day length in September is 12h and 14min.

When is the sunrise / sunset in September in San Juan?

On the first day of September, sunrise is at 6:09 am and sunset at 6:39 pm. On the last day of the month, sunrise is at 6:14 am and sunset at 6:14 pm AST.

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

The average sunshine duration in September in San Juan is 9.4h.

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

April through November, with an average maximum UV index of 7, are months with the highest UV index.

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

In September, the average daily maximum UV index in San Juan, Puerto Rico, is 7. A UV Index reading of 6 to 7 represents a high health risk from exposure to Sun's UV rays.

Average temperature in September
San Juan, PR

Average temperature in September - San Juan, PR
  • Average high temperature in September: 84.9°F

The warmest month (with the highest average high temperature) is August (85.1°F).
The months with the lowest average high temperature are January and March (79.9°F).

  • Average low temperature in September: 79.2°F

The months with the highest average low temperature are August, September and October (79.2°F).
The coldest month (with the lowest average low temperature) is March (73.9°F).

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Average pressure in September
San Juan, PR

Average pressure in September - San Juan, PR
  • Average pressure in September: 29.92"Hg

The months with the highest atmospheric pressure are January and February (30.02"Hg).
The month with the lowest atmospheric pressure is October (29.9"Hg).

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Average wind speed in September
San Juan, PR

Average wind speed in September - San Juan, PR
  • Average wind speed in September: 8.1mph

The windiest month (with the highest average wind speed) is July (10.7mph).
The calmest month (with the lowest average wind speed) is October (7.4mph).

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Average humidity in September
San Juan, PR

Average humidity in September - San Juan, PR
  • Average humidity in September: 78%

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

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Average rainfall in September
San Juan, PR

Average rainfall in September - San Juan, PR
  • Average rainfall in September: 1.18"

The wettest month (with the highest rainfall) is November (1.57").
The driest month (with the least rainfall) is April (0.55").

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Average rainfall days in September
San Juan, PR

Average rainfall days in September - San Juan, PR
  • Average rainfall days in September: 11.7 days

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

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Average sea temperature in September
San Juan, PR

Average sea temperature in September - San Juan, PR
  • Average sea temperature in September: 84.9°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).

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Average daylight in September /
Average sunshine in September
San Juan, PR

Average daylight in September / Average sunshine in September - San Juan, PR
  • Average daylight in September: 12h and 14min

The month with the longest days is June (Average daylight: 13h and 13min).
The month with the shortest days is December (Average daylight: 11h and 2min).

  • Average sunshine in September: 9h and 24min

The month with the most sunshine is June (Average sunshine: 10h and 54min).
The month with the least sunshine is December (Average sunshine: 6h and 36min).

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Average sunshine days in September
San Juan, PR

Average sunshine days in September - San Juan, PR
  • Average sunshine days in September: 12.5 days

The month with the most sunshine days is June (13.7 days).
The month with the least sunshine days is November (9.4 days).

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Average UV index in September
San Juan, PR

Average UV index in September - San Juan, PR
  • Average UV index in September: 7

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

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Average cloud cover in September
San Juan, PR

Average cloud cover in September - San Juan, PR
  • Average cloud cover in September: 26

The month with the most cloud cover is December (Cloud cover 35).
The month with the least cloud cover is September (Cloud cover 26).

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Average visibility in September
San Juan, PR

Average visibility in September - San Juan, PR
  • Average visibility in September: 6mi

The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

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