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September Weather in San Isidro, Costa Rica

Last updated: August 23, 2025

In San Isidro, Costa Rica, the average temperature in September hovers around 22°C (72°F). Temperatures can fluctuate, with a minimum of 20°C (68°F) and a maximum of 26°C (78°F). During this month, expect a significant precipitation total of 766 mm (30.1 in) spread over 30 days, contributing to an average humidity level of 81%.

September Temperature in San Isidro

In September in San Isidro, the average temperature is 22°C (72°F). The maximum can reach 26°C (78°F), while the minimum can drop to 20°C (68°F). This pleasant climate makes it an ideal time for travelers to explore the beauty of San Isidro.

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

The chart illustrates September temperature patterns in San Isidro, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In San Isidro, September typically has an average temperature of 22°C (72°F), with highs reaching up to 26°C (78°F) and lows dropping to around 20°C (68°F).
JanFebMarAprMayJunJulAugSepOctNovDec727273737373727272727271
Data source: Temperature data for San Isidro 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 Isidro

In San Isidro in September, the precipitation amount is 766 mm (30.1 in) over the course of 30 days.

September Precipitation Trends in San Isidro

The chart displays monthly precipitation patterns in San Isidro, 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 Isidro, September typically receives around 766 mm (30.1 inches) of precipitation spread over approximately 30 days.
JanFebMarAprMayJunJulAugSepOctNovDec19499120350742663784838766937885354
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Isidro

In San Isidro in September, humidity is 81%. With an average temperature of 22°C (72°F), this humidity feels like a warm, enveloping blanket, making traveling feel both lush and a bit stifling, as the air clings to your skin and every step is accompanied by a gentle sheen of moisture.

September Average Humidity in San Isidro

This chart illustrates the average monthly humidity levels in San Isidro, 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 Isidro 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 Isidro

In San Isidro in September, the maximum UV index is 14, which corresponds to an extreme Exposure Category. The time to burn is just 10 minutes, so it's crucial to take precautions. For the detailed hourly UV index in San Isidro, you can check here.

Maximum UV Index Levels in San Isidro for September

The chart shows the monthly maximum UV Index (UVI) for San Isidro 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 Isidro typically reaches 14, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec121415151514141414141211
Data source: San Isidro 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 Isidro Compares to Other Months

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

This table compares monthly weather conditions in San Isidro, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather22°C (72°F)194 mm (7.6 inches)68%extreme
February Weather22°C (73°F)99 mm (3.9 inches)68%extreme
March Weather23°C (73°F)120 mm (4.7 inches)66%extreme
April Weather23°C (73°F)350 mm (13.8 inches)67%extreme
May Weather23°C (73°F)742 mm (29.2 inches)69%extreme
June Weather23°C (73°F)663 mm (26.1 inches)84%extreme
July Weather22°C (73°F)784 mm (30.8 inches)85%extreme
August Weather22°C (73°F)838 mm (33.0 inches)82%extreme
September Weather22°C (72°F)766 mm (30.1 inches)81%extreme
October Weather22°C (72°F)937 mm (36.9 inches)80%extreme
November Weather22°C (72°F)885 mm (34.8 inches)80%extreme
December Weather22°C (72°F)354 mm (13.9 inches)72%extreme

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