September weather forecastHillsborough, CA
September
Weather in September
The first month of the autumn, September, is also an agreeable month in Hillsborough, California, with temperature in the range of an average high of 70.2°F (21.2°C) and an average low of 56.8°F (13.8°C).Temperature
September is the warmest month, with the temperature often reaching an average high of 70.2°F (21.2°C) and an average low of 56.8°F (13.8°C).Humidity
In September, the average relative humidity is 73%.Rainfall
In September, the rain falls for 3.4 days. Throughout September, 0.16" (4mm) of precipitation is accumulated. Throughout the year, there are 81.5 rainfall days, and 12.8" (325mm) of precipitation is accumulated.Daylight
In Hillsborough, the average length of the day in September is 12h and 25min.On the first day of the month, sunrise is at 6:40 am and sunset at 7:38 pm. On the last day of September, sunrise is at 7:04 am and sunset at 6:53 pm PDT.
Sunshine
In September, the average sunshine is 10.9h.UV index
The months with the highest UV index are June through September, with an average maximum UV index of 5. A UV Index reading of 3 to 5 represents a moderate threat to health from exposure to the Sun's UV radiation for the average person.Note: In September, a daily maximum UV index of 5 leads to the following instructions:
Prioritize safety - Recommendations to avert sunburn are shared. The Sun's radiation is especially intense around midday; try to stay in shade during this period. Your best bet for sun defense on the face, eyes, and neck is a hat with a wide brim.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Hillsborough, CA
- Average high temperature in September: 70.2°F
The warmest month (with the highest average high temperature) is September (70.2°F).
The month with the lowest average high temperature is December (55.6°F).
- Average low temperature in September: 56.8°F
The month with the highest average low temperature is September (56.8°F).
The coldest month (with the lowest average low temperature) is January (47.5°F).
Average pressure in September
Hillsborough, 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
Hillsborough, CA
- Average wind speed in September: 6.1mph
The windiest month (with the highest average wind speed) is April (8.3mph).
The calmest month (with the lowest average wind speed) is September (6.1mph).
Average humidity in September
Hillsborough, CA
- Average humidity in September: 73%
The month with the highest relative humidity is August (78%).
The month with the lowest relative humidity is October (70%).
Average rainfall in September
Hillsborough, CA
- Average rainfall in September: 0.16"
The wettest month (with the highest rainfall) is February (2.44").
The driest month (with the least rainfall) is July (0.08").
Average rainfall days in September
Hillsborough, CA
- Average rainfall days in September: 3.4 days
The month with the highest number of rainy days is March (12.8 days).
The months with the least rainy days are June and July (2.4 days).
Average daylight in September /
Average sunshine in September
Hillsborough, 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: 10h and 54min
The month with the most sunshine is July (Average sunshine: 11h and 48min).
The month with the least sunshine is December (Average sunshine: 5h and 48min).
Average sunshine days in September
Hillsborough, CA
- Average sunshine days in September: 23.2 days
The month with the most sunshine days is July (24.6 days).
The month with the least sunshine days is March (16.3 days).
Average UV index in September
Hillsborough, 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 February and December (UV index 3).
Average cloud cover in September
Hillsborough, CA
- Average cloud cover in September: 15
The month with the most cloud cover is March (Cloud cover 36).
The months with the least cloud cover are July and September (Cloud cover 15).
Average visibility in September
Hillsborough, 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).
