In September, South San Francisco typically sees daytime highs of 21.9°C and overnight lows around 12.1°C. Compared to the annual average high of 17.7°C, September runs +4.3°C.
September in South San Francisco averages a daytime high of 21.9°C and an overnight low of 12.1°C.
September runs +4.3°C compared to South San Francisco's annual average high of 17.7°C, ranking #1 of 12 months by warmth.
Plan for daytime highs near 21.9°C and cooler evenings around 12.1°C.