September weather forecast
Saint Helena, CA

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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.

Frequently asked questions

Is it hot during September?

Saint Helena in September has an average high-temperature of 85.3°F (29.6°C) and an average low-temperature of 54.3°F (12.4°C). The average heat index (a.k.a. 'apparent temperature', 'real feel'), which takes the relative humidity and factors it into the air temperature reading, in September is appraised at 87.8°F (31°C).

What is the least humid month?

September is the least humid month, with an average relative humidity of 53%.

What is the average humidity in September?

The average relative humidity in September is 53%.

How many days does it rain in September?

In Saint Helena, in September, it is raining for 2 days, with typically 0.08" (2mm) of accumulated precipitation.

When it does not snow in Saint Helena?

January, February, April through December are months without snowfall.

What is the average length of the day in September?

In Saint Helena, the average day length in September is 12h and 25min.

What time are sunrise and sunset in September?

On the first day of September, sunrise is at 6:39 am and sunset at 7:39 pm. On the last day of the month, sunrise is at 7:05 am and sunset at 6:53 pm PDT.

How many hours of sunshine does Saint Helena have in September?

In Saint Helena, the average sunshine duration in September is 11h.

How high is the UV index in September?

In September, the average daily maximum UV index is 5. A UV Index estimate of 3 to 5 represents a medium health risk from unsafe exposure to Sun's UV rays.
Average humidity
Average rainfall days
Average snowfall
Average snowfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in September
Saint Helena, CA

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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 / Average sunshine in September - Saint Helena, CA
  • Average daylight in September: 12h and 2min

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 - 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 - 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 - 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 - 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).

Saint Helena, California, USA

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