September weather forecastAtherton, CA
September
Weather in September
September, the first month of the autumn in Atherton, is also an agreeable month, with temperature in the range of an average high of 72.7°F (22.6°C) and an average low of 56.7°F (13.7°C).Temperature
The transition from August to September brings an average high-temperature of a still pleasant 72.7°F (22.6°C), barely different from August's 73°F (22.8°C). The mean low-temperature during September nights is a refreshing 56.7°F (13.7°C).Humidity
In September, the average relative humidity is 69%.Rainfall
In Atherton, in September, it is raining for 2.4 days, with typically 0.12" (3mm) of accumulated precipitation. Throughout the year, there are 73.4 rainfall days, and 11.89" (302mm) of precipitation is accumulated.Daylight
The average length of the day in September is 12h and 25min.On the first day of September, sunrise is at 6:39 am and sunset at 7:37 pm. On the last day of the month, sunrise is at 7:04 am and sunset at 6:52 pm PDT.
Sunshine
In Atherton, California, the average sunshine in September is 11h.UV index
June through September, with an average maximum UV index of 5, are months with the highest UV index. A UV Index estimate of 3 to 5 represents a moderate threat to health from exposure to the Sun's UV rays for the average person.Note: The UV index of 5 in September translates into these instructions:
Prioritize safety - The need to safeguard skin and eyes from harm is emphasized. Avoiding direct sun during mid-day hours can prevent harmful UV radiation exposure. Safeguard your eyes, ears, and face from sun rays with the aid of a wide-brim hat.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Atherton, CA
- Average high temperature in September: 72.7°F
The warmest months (with the highest average high temperature) are July and August (73°F).
The month with the lowest average high temperature is December (55.9°F).
- Average low temperature in September: 56.7°F
The month with the highest average low temperature is September (56.7°F).
The coldest month (with the lowest average low temperature) is February (46°F).
Average pressure in September
Atherton, CA
- Average pressure in September: 29.92"Hg
The month with the highest atmospheric pressure is January (30.13"Hg).
The month with the lowest atmospheric pressure is September (29.92"Hg).
Average wind speed in September
Atherton, CA
- Average wind speed in September: 5.5mph
The windiest month (with the highest average wind speed) is April (7.5mph).
The calmest months (with the lowest average wind speed) are August, September and October (5.5mph).
Average humidity in September
Atherton, CA
- Average humidity in September: 69%
The month with the highest relative humidity is March (75%).
The month with the lowest relative humidity is October (68%).
Average rainfall in September
Atherton, CA
- Average rainfall in September: 0.12"
The wettest month (with the highest rainfall) is February (2.36").
The driest months (with the least rainfall) are July and August (0.04").
Average rainfall days in September
Atherton, CA
- Average rainfall days in September: 2.4 days
The month with the highest number of rainy days is March (12.8 days).
The month with the least rainy days is August (0.8 days).
Average daylight in September /
Average sunshine in September
Atherton, CA
- Average daylight in September: 12h and 24min
The month with the longest days is June (Average daylight: 14h and 42min).
The month with the shortest days is December (Average daylight: 9h and 36min).
- Average sunshine in September: 11h and 0min
The month with the most sunshine is July (Average sunshine: 12h and 0min).
The month with the least sunshine is December (Average sunshine: 5h and 48min).
Average sunshine days in September
Atherton, CA
- Average sunshine days in September: 26.4 days
The month with the most sunshine days is August (27.6 days).
The month with the least sunshine days is March (17.5 days).
Average UV index in September
Atherton, CA
- Average UV index in September: 5
The months with the highest UV index are June, July, August and September (UV index 5).
The months with the lowest UV index are November and December (UV index 3).
Average cloud cover in September
Atherton, CA
- Average cloud cover in September: 12
The month with the most cloud cover is March (Cloud cover 35).
The month with the least cloud cover is July (Cloud cover 9).
Average visibility in September
Atherton, CA
- Average visibility in September: 6mi
The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
