September weather forecast and climate
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 average temperature fluctuating between 84.9°F (29.4°C) and 79.2°F (26.2°C).

Temperature

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

Heat index

The average heat index is evaluated at a torrid 95.7°F (35.4°C). Take extra precautions, as heat cramps and heat exhaustion are possible. Sustained activity may result in heatstroke.
Note that heat index values are valued for light wind and location in the shade. 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 'real feel', 'apparent temperature', 'felt air temperature', or 'feels like', is a measure that combines both air temperature and relative humidity into a single value that indicates how hot the weather feels. This effect is individual, with diverse people perceiving weather differently for numerous reasons (clothing, pregnancy, 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 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.
The human body cools itself through perspiration, as excessive warmth is removed from the body through sweat evaporation. Under high air temperature and humidity (high heat index) conditions, perspiration is limited, and the perception of heat is increased. 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

The average relative humidity in San Juan is 78%.

Rainfall

In San Juan, in September, during 11.7 rainfall days, 1.18" (30mm) of precipitation is typically accumulated. 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

With an average ocean temperature of 84.9°F (29.4°C), September is the month with the warmest seawater in San Juan.
Note: Water temperature between 77°F (25°C) and 84.2°F (29°C) is regarded as very warm and enjoyable by all. With these temperatures, water activities are pleasurable, without feeling uncomfortable for prolonged periods.

Daylight

The average length of the day in San Juan is 12.2h.

Sunshine

In September, the average sunshine in San Juan is 9.4h.

UV index

April through November, with an average maximum UV index of 7, are months with the highest UV index. A UV Index reading of 6 to 7 represents a high threat to health from unsafe exposure to the UV radiation for ordinary individuals.
Note: The average daily UV index of 7 transform into the following instructions:
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. A wide-brim hat offers excellent sun protection for eyes, ears, face, and neck. Sunglasses with UVA and UVB protection significantly reduce eye damage from sun exposure. Tightly woven, loose-fitting clothes provide additional protection from the Sun. Beware! The reflection of water and sand dramatically increases exposure to the UV rays.
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FAQ

What is the temperature in September in San Juan?

The average high-temperature, in September, is 84.9°F (29.4°C), while the average low-temperature is 79.2°F (26.2°C). The average heat index (a.k.a. 'apparent temperature', 'felt air temperature'), that combines both air temperature and relative humidity, in September is appraised at 95.7°F (35.4°C).

What is the average humidity in September in San Juan?

The average relative humidity in September is 78%.

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

In September, in San Juan, the rain falls for 11.7 days. Throughout September, 1.18" (30mm) of precipitation is accumulated.

What month is the ocean warmest 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.

How warm is the water in September in San Juan?

In September, the average ocean 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?

The average length of the day in September in San Juan, Puerto Rico, is 12.2h.

How many hours of sunshine does San Juan have in September?

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

When is 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 intensity in September in San Juan?

The average daily maximum UV index in September is 7. A UV Index of 6 to 7 symbolizes a high health threat from unsafe exposure to the 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).
Months with the lowest average high temperature are January and March (79.9°F).

  • Average low temperature in September: 79.2°F

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"

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

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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%

Months with the highest relative humidity are May, June and July (79%).
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: 12.2h

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

  • Average sunshine in September: 9.4h

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

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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

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).

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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

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

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