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September Weather in Santiago, Costa Rica

Last updated: August 23, 2025

In September, the average temperature in Santiago, Costa Rica is a comfortable 23°C (74°F). Expect minimums around 18°C (66°F) and maximums reaching 29°C (85°F). With an average humidity of 81%, you’ll feel the warmth throughout the day. Be prepared for precipitation, as 461 mm (18.2 in) may fall over 29 days.

September Temperature in Santiago

In September in Santiago, the average temperature is 23°C (74°F). The maximum can reach 29°C (85°F), while the minimum can be as low as 18°C (66°F). This pleasant weather makes Santiago an ideal destination for travelers seeking mild and enjoyable conditions.

September Weather in Santiago: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Santiago, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Santiago, September typically has an average temperature of 23°C (74°F), with highs reaching up to 29°C (85°F) and lows dropping to around 18°C (66°F).
JanFebMarAprMayJunJulAugSepOctNovDec747576767575757473737374
Data source: Temperature data for Santiago 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 Santiago

In Santiago in September, the total precipitation amount is 461 mm (18.2 in) spread over 29 days.

September Precipitation Trends in Santiago

The chart displays monthly precipitation patterns in Santiago, 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 Santiago, September typically receives around 461 mm (18.2 inches) of precipitation spread over approximately 29 days.
JanFebMarAprMayJunJulAugSepOctNovDec28131811841239729739346163925172
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Santiago

In Santiago in September, humidity is 81%. With an average temperature of 23°C (74°F), this humidity feels like a warm, heavy blanket draped over your skin, making travel feel a bit more sluggish and requiring plenty of water breaks to stay comfortable.

September Average Humidity in Santiago

This chart illustrates the average monthly humidity levels in Santiago, 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 Santiago 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 Santiago

In Santiago 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 Santiago.

Maximum UV Index Levels in Santiago for September

The chart shows the monthly maximum UV Index (UVI) for Santiago 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 Santiago typically reaches 13, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec121315151414141313141210
Data source: Santiago 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 Santiago Compares to Other Months

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

This table compares monthly weather conditions in Santiago, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather23°C (74°F)28 mm (1.1 inches)68%extreme
February Weather24°C (76°F)13 mm (0.5 inches)68%extreme
March Weather25°C (77°F)18 mm (0.7 inches)66%extreme
April Weather24°C (76°F)118 mm (4.6 inches)67%extreme
May Weather24°C (75°F)412 mm (16.2 inches)69%extreme
June Weather24°C (75°F)397 mm (15.6 inches)84%extreme
July Weather24°C (75°F)296 mm (11.7 inches)85%extreme
August Weather23°C (74°F)393 mm (15.5 inches)82%extreme
September Weather23°C (74°F)461 mm (18.2 inches)81%extreme
October Weather23°C (73°F)639 mm (25.2 inches)80%extreme
November Weather23°C (74°F)251 mm (9.9 inches)80%extreme
December Weather23°C (74°F)72 mm (2.8 inches)72%very high

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