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September Weather in San Juan, Costa Rica

Last updated: August 23, 2025

In September, the average temperature in San Juan, Costa Rica hovers around 20°C (69°F), with a comfortable range between 15°C (60°F) and 27°C (80°F). Expect moderate rainfall during this period, with a total precipitation of 436 mm (17.2 in) spread over 28 days. Moreover, the average humidity sits at a lush 81%, creating a uniquely vibrant atmosphere.

September Temperature in San Juan

In September in San Juan, the average temperature is 20°C (69°F). Maximums can reach 27°C (80°F), while minimums can dip as low as 15°C (60°F). This pleasant climate makes it an ideal time for outdoor adventures and exploring all that San Juan has to offer.

September Weather in San Juan: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in San Juan, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In San Juan, September typically has an average temperature of 20°C (69°F), with highs reaching up to 27°C (80°F) and lows dropping to around 15°C (60°F).
JanFebMarAprMayJunJulAugSepOctNovDec686969706969696968686868
Data source: Temperature data for San Juan generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in San Juan

In San Juan in September, the precipitation amount is 436 mm (17.2 in) over the course of 28 days.

September Precipitation Trends in San Juan

The chart displays monthly precipitation patterns in San Juan, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In San Juan, September typically receives around 436 mm (17.2 inches) of precipitation spread over approximately 28 days.
JanFebMarAprMayJunJulAugSepOctNovDec3213157939135123333143657020963
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Juan

In San Juan in September, humidity is 81%. With an average temperature of 20°C (69°F), this humidity feels like a thick blanket embracing you, making travel a bit uncomfortable and sticky.

September Average Humidity in San Juan

This chart illustrates the average monthly humidity levels in San Juan, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in San Juan is approximately 81%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec68%68%66%67%69%84%85%82%81%80%80%73%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in San Juan

In San Juan in September, the maximum UV index reaches 13, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's crucial to take protective measures. For detailed information, you can check the Hourly UV Index in San Juan.

Maximum UV Index Levels in San Juan for September

The chart shows the monthly maximum UV Index (UVI) for San Juan in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in San Juan typically reaches 13, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec121315151414141313141210
Data source: San Juan September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in San Juan Compares to Other Months

Weather in San Juan varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in San Juan, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in San Juan, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather20°C (68°F)32 mm (1.3 inches)68%extreme
February Weather20°C (69°F)13 mm (0.5 inches)68%extreme
March Weather21°C (70°F)15 mm (0.6 inches)66%extreme
April Weather21°C (70°F)79 mm (3.1 inches)67%extreme
May Weather21°C (70°F)391 mm (15.4 inches)69%extreme
June Weather21°C (70°F)351 mm (13.8 inches)84%extreme
July Weather21°C (69°F)233 mm (9.2 inches)85%extreme
August Weather20°C (69°F)331 mm (13.0 inches)82%extreme
September Weather20°C (69°F)436 mm (17.2 inches)81%extreme
October Weather20°C (68°F)570 mm (22.4 inches)80%extreme
November Weather20°C (68°F)209 mm (8.2 inches)80%extreme
December Weather20°C (68°F)63 mm (2.5 inches)72%very high

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