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September Weather in Saint John, United States

Last updated: June 24, 2025

In Saint John, United States, the average temperature in September is a pleasant 20°C (68°F). However, don't be caught off guard! Temperatures can drop as low as 5°C (42°F) and soar to a high of 33°C (92°F). During this month, expect around 74 mm (2.9 in) of precipitation over approximately 8 days. With an average humidity of 80%, be prepared for a bit of a muggy feel in the air.

September Temperature in Saint John

In September in Saint John, the average temperature is 20°C (68°F). Maximum temperatures can reach 33°C (92°F), while minimums can drop to as low as 5°C (42°F). This makes Saint John an ideal destination for travelers looking to enjoy a mix of warm days and cool nights.

September Weather in Saint John: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Saint John, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Saint John, September typically has an average temperature of 20°C (68°F), with highs reaching up to 33°C (92°F) and lows dropping to around 5°C (42°F).
JanFebMarAprMayJunJulAugSepOctNovDec272939486071757368554034
Data source: Temperature data for Saint John 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 Saint John

In Saint John in September, the precipitation amount is 74 mm (2.9 in) over a period of 8 days.

September Precipitation Trends in Saint John

The chart displays monthly precipitation patterns in Saint John, 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 Saint John, September typically receives around 74 mm (2.9 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec70719911916213010392741426960
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Saint John

In Saint John in September, humidity is 80%. With an average temperature of 20°C (68°F), this humidity feels like traveling through a warm, dense blanket that clings to your skin, making you feel both sticky and lethargic as you explore the sights.

September Average Humidity in Saint John

This chart illustrates the average monthly humidity levels in Saint John, 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 Saint John is approximately 80%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec82%83%84%85%79%82%80%81%80%82%88%84%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Saint John

In Saint John in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Saint John.

Maximum UV Index Levels in Saint John for September

The chart shows the monthly maximum UV Index (UVI) for Saint John 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 Saint John typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec34689101098642
Data source: Saint John 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 Saint John Compares to Other Months

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

This table compares monthly weather conditions in Saint John, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-3°C (27°F)70 mm (2.7 inches)82%moderate
February Weather-2°C (29°F)71 mm (2.8 inches)83%moderate
March Weather4°C (39°F)99 mm (3.9 inches)84%high
April Weather9°C (48°F)119 mm (4.7 inches)85%very high
May Weather16°C (60°F)162 mm (6.4 inches)79%very high
June Weather22°C (71°F)130 mm (5.1 inches)82%very high
July Weather24°C (75°F)103 mm (4.1 inches)80%very high
August Weather23°C (73°F)92 mm (3.6 inches)81%very high
September Weather20°C (68°F)74 mm (2.9 inches)80%very high
October Weather13°C (56°F)142 mm (5.6 inches)82%high
November Weather5°C (40°F)68 mm (2.7 inches)88%moderate
December Weather1°C (34°F)60 mm (2.4 inches)84%low

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