September Weather in Jamestown, Saint Helena, Ascension and Tristan da Cunha

Last updated: August 31, 2025

In Jamestown, Saint Helena, Ascension and Tristan da Cunha, the average temperature in September is a pleasant 20°C (67°F). Temperatures can range from a minimum of 18°C (65°F) to a maximum of 21°C (69°F), ensuring a comfortable climate. Expect 13 mm (0.5 in) of precipitation over the course of 1 day, with an average humidity of 78%, creating a refreshing atmosphere.

September Temperature in Jamestown

In September in Jamestown, the average temperature is 20°C (67°F), with maximums reaching 21°C (69°F) and minimums dropping to as low as 18°C (65°F). This comfortable climate makes Jamestown an ideal destination for outdoor activities and sightseeing during this time of year.

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

The chart illustrates September temperature patterns in Jamestown, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Jamestown, September typically has an average temperature of 20°C (67°F), with highs reaching up to 21°C (69°F) and lows dropping to around 18°C (65°F).

Data source: Temperature data for Jamestown generated using information from the Copernicus Climate Change Service.

September Precipitation in Jamestown

In Jamestown in September, the precipitation amount is 13 mm (0.5 in) over the course of 1 day.

September Precipitation Trends in Jamestown

The chart displays monthly precipitation patterns in Jamestown, 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 Jamestown, September typically receives around 13 mm (0.5 inches) of precipitation spread over approximately 1 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

September Humidity in Jamestown

In Jamestown in September humidity is 78%. With an average temperature of 20°C (67°F), this humidity feels like walking through a warm, thick blanket, making travel a bit sticky and requiring frequent breaks to find shade and cool refreshments.

September Average Humidity in Jamestown

This chart illustrates the average monthly humidity levels in Jamestown, 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 Jamestown is approximately 78%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Jamestown

In Jamestown 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 Jamestown.

Maximum UV Index Levels in Jamestown for September

The chart shows the monthly maximum UV Index (UVI) for Jamestown 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 Jamestown typically reaches 11, which falls under the extreme exposure category.

Data source: Jamestown 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 Jamestown Compares to Other Months

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

This table compares monthly weather conditions in Jamestown, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	23°C (73°F)	10 mm (0.4 inches)	79%	extreme
February Weather	24°C (75°F)	12 mm (0.5 inches)	81%	extreme
March Weather	24°C (76°F)	16 mm (0.6 inches)	82%	extreme
April Weather	24°C (75°F)	14 mm (0.6 inches)	81%	extreme
May Weather	23°C (73°F)	12 mm (0.5 inches)	78%	very high
June Weather	22°C (71°F)	14 mm (0.5 inches)	74%	very high
July Weather	21°C (69°F)	12 mm (0.5 inches)	75%	very high
August Weather	20°C (68°F)	14 mm (0.6 inches)	76%	very high
September Weather	20°C (67°F)	13 mm (0.5 inches)	78%	extreme
October Weather	19°C (67°F)	11 mm (0.4 inches)	80%	extreme
November Weather	20°C (68°F)	10 mm (0.4 inches)	81%	extreme
December Weather	21°C (70°F)	10 mm (0.4 inches)	80%	extreme