Contents
- Weather in September
- Frequently asked questions
- Average temperature in September
- Average pressure in September
- Average wind speed in September
- Average humidity in September
- Average rainfall in September
- Average rainfall days in September
- Average daylight in September
- Average sunshine in September
- Average sunshine days in September
- Average UV index in September
- Average cloud cover in September
- Average visibility in September
Weather in September
Temperature
The transition into September is marked with an average high-temperature of a warm 84.6°F (29.2°C), showing an insignificant shift from August's 86.2°F (30.1°C). September is characterized by a distinct thermal shift, with nighttime lows averaging at a refreshing 62.6°F (17°C).Heat index
September's heat index is evaluated at a tropical 86°F (30°C). Ongoing exposure and activity could lead to a state of exhaustion, with a chance of heat cramps.Consider that heat index readings are for situations in the shade and light wind. Exposure to the direct sun might augment heat index values by 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'real feel' or 'apparent temperature', is a single figure representing how weather conditions feel when combining temperature and humidity. The impact of weather is individual, with diverse individuals experiencing it differently due to variations in body mass, height, and activity levels. Consider the fact that direct sun exposure can influence how hot one feels, potentially raising the heat index by 15 Fahrenheit (8 Celsius) degrees. Heat index values are highly critical to babies and toddlers. Young individuals are generally in more danger than adults due to their lower capacity to sweat. Moreover, their large skin surface in relation to their small bodies and the increased heat generation from their activities makes them more vulnerable.
Humidity
In September, the average relative humidity is 49%.Rainfall
In Altadena, in September, during 3 rainfall days, 0.16" (4mm) of precipitation is typically accumulated. In Altadena, during the entire year, the rain falls for 52 days and collects up to 8.82" (224mm) of precipitation.Daylight
In Altadena, the average length of the day in September is 12h and 22min.On the first day of the month, sunrise is at 6:26 am and sunset at 7:17 pm. On the last day of September, sunrise is at 6:46 am and sunset at 6:37 pm PDT.
Sunshine
In Altadena, the average sunshine in September is 10.8h.UV index
The months with the highest UV index are June through September, with an average maximum UV index of 6. A UV Index reading of 6 to 7 represents a high threat to health from unprotected exposure to Sun's UV rays for average individuals.Note: The UV index of 6 during September leads to these advisories:
Eschew overexposure. Those with light skin may suffer burns in fewer than 20 minutes. Stay in the shade and limit direct Sun exposure from 10 a.m. to 4 p.m., a time when UV radiation is particularly strong. Remember, however, that shade structures may not provide complete protection. Sunglasses that ward off UVA and UVB rays play a pivotal role in reducing solar eye damage.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
How hot is September?
What is the average humidity in September?
How many days does it rain in September?
What is the average length of the day in September?
What time are sunrise and sunset in September?
How many hours of sunshine does Altadena have in September?
What are the months with the highest UV index in Altadena?
What is the UV index reading in September in Altadena?
Average temperature in September
Altadena, CA
- Average high temperature in September: 84.6°F
The warmest month (with the highest average high temperature) is August (86.2°F).
The month with the lowest average high temperature is December (61°F).
- Average low temperature in September: 62.6°F
The month with the highest average low temperature is August (64.4°F).
The coldest month (with the lowest average low temperature) is December (45.5°F).
Average pressure in September
Altadena, CA
- Average pressure in September: 29.89"Hg
The month with the highest atmospheric pressure is January (30.11"Hg).
The month with the lowest atmospheric pressure is June (29.88"Hg).
Average wind speed in September
Altadena, CA
- Average wind speed in September: 4.4mph
The windiest month (with the highest average wind speed) is April (5.8mph).
The calmest month (with the lowest average wind speed) is September (4.4mph).
Average humidity in September
Altadena, CA
- Average humidity in September: 49%
The months with the highest relative humidity are March, May and June (56%).
The month with the lowest relative humidity is November (46%).
Average rainfall in September
Altadena, CA
- Average rainfall in September: 0.16"
The wettest month (with the highest rainfall) is February (1.81").
The driest month (with the least rainfall) is June (0.04").
Average rainfall days in September
Altadena, CA
- Average rainfall days in September: 3 days
The month with the highest number of rainy days is March (7.5 days).
The month with the least rainy days is June (1.3 days).
Average daylight in September /
Average sunshine in September
Altadena, CA
- Average daylight in September: 12h and 2min
The month with the longest days is June (Average daylight: 14h and 24min).
The month with the shortest days is December (Average daylight: 9h and 54min).
- Average sunshine in September: 10h and 5min
The months with the most sunshine are June and July (Average sunshine: 12h and 6min).
The months with the least sunshine are February and December (Average sunshine: 6h and 54min).
Average sunshine days in September
Altadena, CA
- Average sunshine days in September: 25.6 days
The month with the most sunshine days is June (27.2 days).
The month with the least sunshine days is February (21.3 days).
Average UV index in September
Altadena, CA
- Average UV index in September: 6
The months with the highest UV index are June, July, August and September (UV index 6).
The month with the lowest UV index is December (UV index 3).
Average cloud cover in September
Altadena, CA
- Average cloud cover in September: 6
The month with the most cloud cover is March (Cloud cover 22).
The month with the least cloud cover is August (Cloud cover 5).
Average visibility in September
Altadena, 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).
Altadena, California, USA
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