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September Weather in Johnston, United States

Last updated: June 24, 2025

In Johnston, United States, the average temperature in September hovers around 20°C (69°F), making it a pleasant time to visit. Expect a range where the minimum dips to 4°C (40°F) and the maximum can soar up to 34°C (94°F). Precipitation averages 120 mm (4.7 in) over 10 days, while the ambiance is often accompanied by an average humidity of 73%. Be prepared for a mix of weather as you explore this charming destination!

September Temperature in Johnston

In September in Johnston, the average temperature is 20°C (69°F). Maximums can reach 34°C (94°F), and minimums can be as low as 4°C (40°F). This makes it a great time to explore Johnston, as you'll experience mild weather with the potential for warm days and cooler nights.

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

The chart illustrates September temperature patterns in Johnston, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Johnston, September typically has an average temperature of 20°C (69°F), with highs reaching up to 34°C (94°F) and lows dropping to around 4°C (40°F).
JanFebMarAprMayJunJulAugSepOctNovDec222339496274777468523830
Data source: Temperature data for Johnston 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 Johnston

In Johnston in September, the precipitation amount is 120 mm (4.7 in) spread over a duration of 10 days.

September Precipitation Trends in Johnston

The chart displays monthly precipitation patterns in Johnston, 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 Johnston, September typically receives around 120 mm (4.7 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec3740817516910976871201283937
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Johnston

In Johnston in September humidity is 73%. With an average temperature of 20°C (69°F), this humidity feels like a warm embrace, making travel slightly sticky but ultimately comfortable as long as you stay hydrated and take breaks in the shade.

September Average Humidity in Johnston

This chart illustrates the average monthly humidity levels in Johnston, 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 Johnston is approximately 73%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec78%80%77%78%77%81%81%77%73%75%85%83%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Johnston

In Johnston 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 Johnston.

Maximum UV Index Levels in Johnston for September

The chart shows the monthly maximum UV Index (UVI) for Johnston 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 Johnston typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec35689111098643
Data source: Johnston 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 Johnston Compares to Other Months

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

This table compares monthly weather conditions in Johnston, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-6°C (22°F)37 mm (1.4 inches)78%moderate
February Weather-5°C (23°F)40 mm (1.6 inches)80%moderate
March Weather4°C (40°F)81 mm (3.2 inches)77%high
April Weather9°C (49°F)75 mm (2.9 inches)77%very high
May Weather17°C (62°F)169 mm (6.7 inches)77%very high
June Weather23°C (74°F)109 mm (4.3 inches)81%extreme
July Weather25°C (77°F)76 mm (3.0 inches)81%very high
August Weather23°C (74°F)87 mm (3.4 inches)77%very high
September Weather20°C (69°F)120 mm (4.7 inches)73%very high
October Weather11°C (53°F)128 mm (5.0 inches)75%high
November Weather3°C (39°F)39 mm (1.5 inches)85%moderate
December Weather-1°C (31°F)37 mm (1.5 inches)83%moderate

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