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September Weather in San Juan, Mexico

Last updated: August 27, 2025

In September, the average temperature in San Juan, Mexico is a warm 28°C (83°F). However, be prepared for a range, as it can dip to 18°C (65°F) and soar as high as 40°C (104°F). Expect precipitation of 119 mm (4.7 in) over approximately 12 days, accompanied by an average humidity of 75%. Enjoy your time in this vibrant locale! 🌞

September Temperature in San Juan

In September in San Juan, the average temperature is 28°C (83°F). The maximum can reach 40°C (104°F), and the minimum can be as low as 18°C (65°F). Travelers should prepare for warm weather with potential heat peaks, making it a great time for beach activities and exploring the outdoors, while also ensuring to stay hydrated and protected from the sun.

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 28°C (83°F), with highs reaching up to 40°C (104°F) and lows dropping to around 18°C (65°F).
JanFebMarAprMayJunJulAugSepOctNovDec616573788386878882766863
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 total precipitation amount is 119 mm (4.7 in), falling over a span of 12 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 119 mm (4.7 inches) of precipitation spread over approximately 12 days.
JanFebMarAprMayJunJulAugSepOctNovDec2014254686867816119562320
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 75%. With an average temperature of 28°C (83°F), this humidity feels like a warm blanket enveloping you, making outdoor activities feel particularly heavy, and prompting frequent breaks in the shade to stay comfortable while traveling.

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 75%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%83%78%81%82%74%68%67%75%78%83%86%
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 11, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's essential to take precautions. For more details, 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 11, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec68101212121212111076
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 Weather16°C (61°F)20 mm (0.8 inches)84%high
February Weather18°C (65°F)13 mm (0.5 inches)83%very high
March Weather23°C (73°F)25 mm (1.0 inches)78%very high
April Weather25°C (78°F)46 mm (1.8 inches)81%extreme
May Weather28°C (83°F)86 mm (3.4 inches)82%extreme
June Weather30°C (86°F)86 mm (3.4 inches)74%extreme
July Weather31°C (87°F)78 mm (3.1 inches)68%extreme
August Weather31°C (89°F)16 mm (0.6 inches)67%extreme
September Weather28°C (83°F)119 mm (4.7 inches)75%extreme
October Weather24°C (76°F)56 mm (2.2 inches)78%very high
November Weather20°C (68°F)23 mm (0.9 inches)83%high
December Weather17°C (64°F)20 mm (0.8 inches)86%high

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