San Diego
California, USA
Long-term weather forecast
Long-term weather forecast
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September weather forecast and Climate
San Diego, CA

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The view of Coronado Island in San Diego, California, from across a water body on a sidewalk, with a row of palm trees
The view of Coronado Island in San Diego, California, from across a water body on a sidewalk, with a row of palm trees
September sees the average temperatures in the 65°F (18.3°C) to 76°F (24.4°C), and the warm days are an extension of the summer season. The heat can rise above 80°F (26.7°C) on a few days while most are above 60°F (15.6°C). Nights are comfortable, but there is a rare chance of the temperature dropping below 55°F (12.8°C).
September is usually dry, and the month has a history of high temperatures, including the record high of 111°F (43.9°C). Expect ample sunshine with a mild breeze in the evening, but wear sun protection when the sun is strong during midday.
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  • The average high temperature in September: 75.9°F

The warmest month (with the highest average high temperature) is August (76.4°F).
The month with the lowest average high temperature is December (64.7°F).

  • The average low temperature in September: 65.2°F

The month with the highest average low temperature is August (66.7°F).
The coldest month (with the lowest average low temperature) is December (48.4°F).

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  • The average humidity in September: 72.7%

The month with the highest relative humidity is July (74.6%).
The month with the lowest relative humidity is January (63.1%).

  • The average rainfall in September: 0.2"

The wettest month (with the highest rainfall) is January (2.1").
The driest month (with the lowest rainfall) is July (0").

  • The average rainfall days in September: 1.2 days

The month with the highest number of rainy days is February (7.1 days).
The month with the lowest number of rainy days is August (0.4 days).

  • The average sea temperature in September: 66.7°F

The best month for swimming (with the highest average sea temperature) is August (67.9°F).
The coldest month (with the lowest average sea temperature) is February (58.7°F).

  • The average daylight in September: 12h

Months with the longest days are May, June and July (Average daylight: 14h).
Months with shortest days are January, November and December (Average daylight: 10h).

  • The average sunshine in September: 8.4h

The month with most sunshine is July (Average sunshine: 9.8h).
The month with least sunshine is December (Average sunshine: 7.5h).

  • The average UV index in September: 8

Months with the highest UV index are June, July and August (UV index 10).
Months with the lowest UV index are January and December (UV index 3).

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