September weather forecastSaint Helena, CA
September
Weather in September
The first month of the autumn, September, is also a moderately hot month in Saint Helena, California, with an average temperature ranging between max 85.3°F (29.6°C) and min 54.3°F (12.4°C).Temperature
The onset of September brings an average high-temperature of a warm 85.3°F (29.6°C), nearly matching the August temperature. Throughout September, Saint Helena acknowledges a distinct difference between its daytime highs and the steady low average of 54.3°F (12.4°C).Heat index
In September, the heat index is appraised at a tropical 87.8°F (31°C). Enduring exposure and unrelenting activity might cause a state of weariness, potentially leading to heat cramps.In terms of the heat index, values are set with light wind and shade conditions in mind. The heat index has the possibility to be enhanced by 15 Fahrenheit (8 Celsius) degrees when there is direct sun exposure.
Note: The heat index, also known as 'real feel' or 'felt air temperature', is an indicator that blends the effects of temperature and humidity to depict perceived warmth. The influence of weather is personal, with a diverse population experiencing it differently due to differences in body mass, stature, and degree of activity. When exposed to direct sunlight, it's possible for the heat index to increase by as much as 15 Fahrenheit (8 Celsius) degrees. Heat index values are highly critical to babies and toddlers. Young children typically face greater hazards than adults because they do not sweat as much. Their larger skin surface in comparison to their little bodies and the high heat production from their active nature compounds their vulnerability.
Humidity
With an average relative humidity of 53%, September is the least humid month.Rainfall
In Saint Helena, in September, during 2 rainfall days, 0.08" (2mm) of precipitation is typically accumulated. Throughout the year, there are 76.2 rainfall days, and 16.93" (430mm) of precipitation is accumulated.Snowfall
In Saint Helena, snow does not fall in January, February, April through December.Daylight
In Saint Helena, California, the average length of the day in September is 12h and 25min.On the first day of the month, sunrise is at 6:39 am and sunset at 7:39 pm. On the last day of September, sunrise is at 7:05 am and sunset at 6:53 pm PDT.
Sunshine
The average sunshine in September is 11h.UV index
In Saint Helena, the average daily maximum UV index in September is 5. A UV Index value of 3 to 5 symbolizes a medium vulnerability from unprotected exposure to Sun's UV rays for the ordinary person.Note: An average UV index of 5 in September transforms into this advice:
Exercise caution. The susceptibility of light skin individuals to burns is less than 30 minutes. Direct exposure to the Sun's intense radiation around midday should be avoided for health reasons. Boost your sun resistance with garments that are densely woven yet spacious.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Saint Helena, CA
- Average high temperature in September: 85.3°F
The warmest month (with the highest average high temperature) is July (88.3°F).
The month with the lowest average high temperature is December (54.5°F).
- Average low temperature in September: 54.3°F
The month with the highest average low temperature is September (54.3°F).
The coldest month (with the lowest average low temperature) is December (39.6°F).
Average pressure in September
Saint Helena, CA
- Average pressure in September: 29.91"Hg
The month with the highest atmospheric pressure is January (30.14"Hg).
The months with the lowest atmospheric pressure are June, August and September (29.91"Hg).
Average wind speed in September
Saint Helena, CA
- Average wind speed in September: 4.6mph
The windiest month (with the highest average wind speed) is May (5.8mph).
The calmest month (with the lowest average wind speed) is November (4.3mph).
Average humidity in September
Saint Helena, CA
- Average humidity in September: 53%
The month with the highest relative humidity is March (76%).
The month with the lowest relative humidity is September (53%).
Average rainfall in September
Saint Helena, CA
- Average rainfall in September: 0.08"
The wettest month (with the highest rainfall) is February (3.7").
The driest month (with the least rainfall) is July (0").
Average rainfall days in September
Saint Helena, CA
- Average rainfall days in September: 2 days
The month with the highest number of rainy days is March (13.5 days).
The month with the least rainy days is August (0.3 days).
Average snowfall in September
Saint Helena, CA
- Average snowfall in September: 0"
The month with the highest snowfall is March (0.04").
The months with the least snowfall are January, February, April, May, June, July, August, September, October, November and December (0").
Average snowfall days in September
Saint Helena, CA
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is March (0.2 days).
The months with the least snowfall days are January, February, April, May, June, July, August, September, October, November and December (0 days).
Average daylight in September /
Average sunshine in September
Saint Helena, CA
- Average daylight in September: 12h and 24min
The month with the longest days is June (Average daylight: 14h and 48min).
The month with the shortest days is December (Average daylight: 9h and 30min).
- Average sunshine in September: 11h and 0min
The month with the most sunshine is July (Average sunshine: 11h and 54min).
The month with the least sunshine is December (Average sunshine: 5h and 18min).
Average sunshine days in September
Saint Helena, CA
- Average sunshine days in September: 27.5 days
The month with the most sunshine days is July (30 days).
The month with the least sunshine days is March (15.9 days).
Average UV index in September
Saint Helena, CA
- Average UV index in September: 5
The months with the highest UV index are June, July and August (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 3).
Average cloud cover in September
Saint Helena, CA
- Average cloud cover in September: 10
The month with the most cloud cover is March (Cloud cover 44).
The month with the least cloud cover is July (Cloud cover 7).
Average visibility in September
Saint Helena, CA
- Average visibility in September: 6mi
The months with the highest visibility are February, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January and March (5mi).
