September weather forecast
Pasadena, CA

September squeezes the summer in Pasadena a bit more, maintaining an average high temperature of 84.4°F (29.1°C). As the year progresses towards its end, the weather in September stays relatively warm but introduces the onset of cooler nights. Despite the slight drop in temperature, the ample sunshine ensures a bright and vibrant atmosphere. The headway into autumn does not deter outdoor activities, allowing residents and visitors to continue soaking the sun. September holds onto the remnants of summer, giving Pasadena one last full month of sunshine and warmth before easing into fall.

Temperature

Pasadena's weather in September displays an average high-temperature of a moderately hot 84.4°F (29.1°C), showing minor disparity from August's 87.1°F (30.6°C). Throughout September, Pasadena registers a consistent average low-temperature of 63.3°F (17.4°C).

Heat index

September's mean heat index is appraised at a hot 86°F (30°C). Prolonged exposure combined with continuous activity could lead to exhaustion, and possibly heat cramps.
The metrics for the heat index are tailored for both shady environments and light winds. The heat index might be elevated by 15 Fahrenheit (8 Celsius) degrees due to direct sun exposure.
Note: The heat index, also known as 'real feel' or 'apparent temperature', is an indicator that blends the effects of temperature and humidity to depict perceived warmth. This effect tends to be personal, with the weather perception differing among individuals due to variations in body mass, height, and exertion. Under direct sun rays, the felt temperature might be heightened, with the heat index increasing by 15 Fahrenheit (8 Celsius) degrees. Heat index values are highly important for children. Young children are more at risk than adults since they tend to sweat less. Moreover, their large skin surface in proportion to their small bodies and the high heat production due to their activities contribute to their vulnerability.

Humidity

In Pasadena, the average relative humidity in September is 50%.

Rainfall

In Pasadena, in September, it is raining for 2.6 days, with typically 0.16" (4mm) of accumulated precipitation. Throughout the year, there are 50.1 rainfall days, and 8.5" (216mm) of precipitation is accumulated.

Daylight

In September, the average length of the day is 12h and 22min.
On the first day of September, sunrise is at 6:26 am and sunset at 7:17 pm. On the last day of the month, sunrise is at 6:46 am and sunset at 6:37 pm PDT.

Sunshine

The average sunshine in September in Pasadena is 10.8h.

UV index

June through September, with an average maximum UV index of 6, are months with the highest UV index in Pasadena. A UV Index value of 6 to 7 symbolizes a high threat to health from unprotected exposure to Sun's UV rays for the ordinary person.
Note: In September, the maximum UV index of 6 transforms into these recommendations:
Take precautions and utilize sun safety practices. Protection against skin and eye damage is required. Avoid exposure to the Sun and try to stay in the shade between 10 a.m. and 4 p.m., when UV radiation is most potent, but be aware that parasols or canopies may not offer full protection. Your best bet for sun defense on the face, eyes, and neck is a hat with a wide brim.